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Another bogging/lugging problem
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PostPosted: Thu Apr 08, 2021 11:53 am    Post subject: Another bogging/lugging problem Reply with quote

Hoping you can help me put together a checklist to try to resolve the problem (engine specs and symptoms below)...

Engine specs.
Newly rebuilt (by me last year) 1600 type 1 dual port. Built to stock 1971 bus engine specs (the case is a 71 bus case) with 7.5 compression ratio.
Empi 34 PICT 3 carb that has about 1000 miles on it.
Bosch 034 SVDA distributor with points and condenser.
Pierburg flat-top fuel pump.
Empi stock 1600 heads. Kolbenschmidt barrels and pistons. NOS VW camshaft. 12V electrics. Oil bath air cleaner.

Installed in my '56 splitty single cab running a '67 transaxle with reduction boxes.

The engine has about 500 miles on it since the rebuild, mostly done last autumn before it was laid up for the winter. I noticed the problem then, but it didn't seem as bad as it does now.

The fuel system was completely replaced about five years ago, including a new fuel tank. There's no crud in the system. The fuel has sta-bil fuel stabiliser in it from when it was laid up.

It's fine pulling away in first and buzzing round town in 3rd @ 20-40mph. It sits happily at 50-60 and more on a fast road. I've had it up to 70 for a short spurt to make sure it didn't grenade on me and it was happy with that too.

It warms up nicely and the manifold heat risers get hot. I cleaned them as a precaution during the rebuild.

The problem

Serious bogging issue accellerating from low speeds in 2nd.

The issue is most noticeable when turning across traffic in to side roads, pulling away from a local railway crossing and joining roundabouts (i.e nowhere that I want to get stuck without power to pull away).

I'll be slow or slowiing, but going too quickly to shift down to first without crunching the gearbox, so I leave it in second. When I hit the accellerator to pull away again it bogs (no power) and stutters/stumbles. It feels like it will cut out or backfire if I keep the throttle open, so I dip the clutch and rev it. Then it'll pull away fine.

It also feels like it stumbles a little if I try to accellerate too quickly in 2nd or 3rd while the engine is stone cold, but I've been assuming that was just due to the engine being cold and still on choke. I haven't noticed that problem when it warms up.


I live in a residential street. Out of respect for my neighbours, I want to try to eliminate as many possible causes as it's practical to do without running and revving the engine on the drive.

On my checklist for the weekend so far

>Check distributor vacuum. It was fine when I rebuit the engine, but I guess it could have suddenly gone bad.
>Check the points for pitting/burning and gap.
>Check all the plugs for signs of lean or rich condition.
>Check accellerator pump to make sure it squirts immediately. If so, I'll check the squirt volume too.
>Check for vacuum leaks. I've read that bogging can be a lean-running symptom. I pressure-tested the intake and carb when the engine went back in and it was fine, but I'll do it again.
>Check the exhaust for leaks at the head, in case that's causing lean running. I had one of the heat exchanger-to-head connections come loose in the first 300 miles. I replaced the nuts and it seemed fine the other week when I checked it again.

Is it worth checking compression?
Is it worth running the tune up procedure again?
What else should I check?

Thanks
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PostPosted: Thu Apr 08, 2021 12:33 pm    Post subject: Re: Another bogging/lugging problem Reply with quote

I'm sure others will tell you to change your distributor and check your valves and what not..

I will say that it really sounds like she want's a bigger idle jet.

I solve exactly your issue on plenty of customer motors by going up on idle jet size.

55 now? go to a 60..
60 now? go to a 65.

Easy to swap them out with a screw driver and test.
Few dollars each.

It will make it a dream to drive and totally eliminate stumbles and flat spots.
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PostPosted: Thu Apr 08, 2021 1:59 pm    Post subject: Re: Another bogging/lugging problem Reply with quote

You have all the usual bases covered except... exhaust. What are you running and does it give proper flow through the heat riser? Yes it's warm but is it warm enough?

Is the exhaust tubing too large? And is it a system that pairs the two right ports and the two left ports? Like the dual cannons? Some Vintage Speed exhausts are like that.
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PostPosted: Thu Apr 08, 2021 6:25 pm    Post subject: Re: Another bogging/lugging problem Reply with quote

Ohio Tom wrote:
I'm sure others will tell you to change your distributor and check your valves and what not..

I will say that it really sounds like she want's a bigger idle jet.

I solve exactly your issue on plenty of customer motors by going up on idle jet size.

55 now? go to a 60..
60 now? go to a 65.

Easy to swap them out with a screw driver and test.
Few dollars each.

It will make it a dream to drive and totally eliminate stumbles and flat spots.


^^^^this^^^^

By all means, verify your timing, check the pump jet, and check for vacuum leaks first. If everything checks out, experiment with idle jets. I usually readjust the carb mixture screw for the best lean idle, and air bypass for rpm after each change. I recently experimented with an otherwise stock 1600 single port, and got the best power/mileage with a 60 idle.
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PostPosted: Fri Apr 09, 2021 1:25 am    Post subject: Re: Another bogging/lugging problem Reply with quote

Thanks all.

Oprn - the exhaust is a stock style Jopex. The only unusual thing about the exhaust setup is that one of the heat exchangers has a repair stub on the end, so the outled from cylinder 1 is slightly smaller than the other three at the exhaust.

Ohio Tom and gkeeton - Thanks for the suggestion on jetting. I've had a look at the progressive refinements book for carburetors and it does say that the bus version of the 34 PICT-3 carb should have a g60 pilot jet, so that would make sense.

(It also says 67.5 in brackets after. Does that mean it might need a jet anywhere between 60 and 67.5? I can't find a footnote that explains)

The paperwork that comes with the Empi says it shipped with a 55 idle jet installed , but comes with a 60 as well. I don't remember fitting the larger jet. I'll check that too.


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PostPosted: Fri Apr 09, 2021 2:01 am    Post subject: Re: Another bogging/lugging problem Reply with quote

Check that your coil is actually giving the voltage it is supposed to.
Check that the distributor advances in the window of right. - and that the can is actually advancing the timing.
That the air cleaner is clean and can supply the air needed.
Then increase main jet with 0,5, maybe 0,75
Besides that I almost always increase idle timing to 10 degrees which helps a lot. If timing at 3000 is above 31 degtrees w.o. vacum you need to limt the advance a tad.
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PostPosted: Fri Apr 09, 2021 6:29 am    Post subject: Re: Another bogging/lugging problem Reply with quote

I have run into several SVDA distributors lately (copies) that suck the diaphragm out of them in a very short amount of time (some while still on the run stand, some a few hundred miles later). Like Alstrup said, check that it is actually advancing. If the diaphragm is bad, not only will it not advance, but will give you a small vacuum leak as well. After that, I would do what Ohio Tom said and bump up the idle jet a step. Let us know what fixes it for you
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PostPosted: Fri Apr 09, 2021 6:46 am    Post subject: Re: Another bogging/lugging problem Reply with quote

Ohio Tom wrote:
I solve exactly your issue on plenty of customer motors by going up on idle jet size.

55 now? go to a 60..
60 now? go to a 65.

Easy to swap them out with a screw driver and test.
Few dollars each.

It will make it a dream to drive and totally eliminate stumbles and flat spots.

+1 on this. I opened up a 55 idle jet a tiny bit with a welding tip cleaner and it made a world of difference. I don't recommend that way but it worked (get a new jet or use a jet reamer).
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PostPosted: Sat Apr 10, 2021 8:01 am    Post subject: Re: Another bogging/lugging problem Reply with quote

OK. I feel there is a little improvement, but the problem is not fixed.

I only had a little time this afternoon, but...

>I checked for intake and exhaust leaks (none).
>Confirmed that the distributor vacuum is working smoothly. The can holds a vacuum for at least 60 seconds. Given this is an issue when accelerating, I think that's fine?
>The carb accelerator pump squirts instantly with the slightest movement of the throttle. I adjusted the jet so the jet just hits the cast arm below the air corrector jet to get some 'splash' in case fuel was pooling in the bottom of the manifold
>I checked the air cleaner - the oil is at the right level and it's is pretty clean with some normal debris that show it's doing it's job. The throat flap opens easily and the bob weight closes it correctly.

Given that was all OK, I swapped in the 60 pilot jet and took it for a test drive. The engine felt a little more 'gutsy' even from stone cold and the flat spot isn't quite so severe, but it's still there. Strangely the engine sounded quieter while idling, but I might be imagining that.

If I slow right down to the bottom of the 2nd or 3rd rev range and floor it; there's an initial lurch as it reacts but it doesn't pull smoothly from there. Even keeping my foot to the floor it struggles and picks up slowly until the revs build and then it pulls strongly.

It doesn't feel like it wants to cut out completely any more with my foot to the floor, but it doesn't pick up smoothly and progressively.

I don't think I'm expecting too much of the engine. I'm running a transaxle with reduction boxes and it's an unladen single cab, not a heavily-loaded camper, so I think it should be able to cope.

I didn't get a chance to tune the carb again after swapping the jet, but would that fix the issue, or do I need to consider going up another jet size?

Or should I be looking for another issue entirely?



I didn't have time to
>do a full tune up, but it was tuned a few hundred miles ago and the valves were adjusted again a dozen or so miles ago
>check the compression. I have a leak-down tester, so I may do that for peace of mind tomorrow if anyone thinks that might be a cause.
>check the coil

I did note that there the oil in the engine and in the air cleaner smells of fuel. The oil level doesn't rise, so I don't think the fuel pump is leaking and it was rebuilt not many miles ago anyhow. That might just be the effect of me messing with the throttle while the engine isn't running but could the problem be overfuelling rather than underfuelling?
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PostPosted: Sat Apr 10, 2021 8:21 am    Post subject: Re: Another bogging/lugging problem Reply with quote

Who.Me? wrote:
I didn't get a chance to tune the carb again after swapping the jet, but would that fix the issue, or do I need to consider going up another jet size?

Or should I be looking for another issue entirely?


Readjusting the mixture/idle settings upon the jet change will allow you to get the full results of the change. Simply adding fuel appeared to help, but this is creating issues for the carb that was adjusted for less fuel. Once the carb has been readjusted, then you can experiment further with a larger jet to see if that creates any more improvement.

Who.Me? wrote:
could the problem be overfuelling rather than underfuelling?


If the small increase in jet size has helped the issue, the hesitation is created by a lean mixture.

Addition: After reading frenchroast’s comment below, it got me also thinking about your pump jet adjustment. There seems to open up a can of worms here about whether the pump stream should be on the vent tube to create a splatter for the intake vacuum to pull in, or if it should squirt past the opening butterfly at the rear of the carb throat. I prefer the squirting past the butterfly, but again, that’s something to experiment with.


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PostPosted: Sat Apr 10, 2021 8:23 am    Post subject: Re: Another bogging/lugging problem Reply with quote

Who.Me? wrote:
OK. I feel there is a little improvement, but the problem is not fixed.[/b]

Before I started dialing-in the jets, I made sure there weren't any vacuum leaks, the throttle plate was set right, and the accelerator pump was working normally. Can't remember if you said you did that already. I also bumped up the main jet from a 120 to a 125 before tweaking the idle jet. I left the air correction jet alone. Stock air cleaner, valve lash, coil and wire resistance, dwell, timing checked, flaky condensor replaced, etc. Hope you can get it fixed. It's so nice when after going through everything multiple times you finally get it nailed.
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PostPosted: Sat Apr 10, 2021 9:36 am    Post subject: Re: Another bogging/lugging problem Reply with quote

Is your throttle valve fully-fully closed at hot idle?

If you unplug the fuel cut-off solenoid, how does that change things when driving? How is the wiring to the solenoid?

might as well: fuel pump pressure and volume. I'm kinda just grabbin' hay.
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PostPosted: Mon Apr 12, 2021 7:18 am    Post subject: Re: Another bogging/lugging problem Reply with quote

I had some time today to test the accelerator pump and have some strange results.

The pump was set to minimum and was delivering about 0.85cc/stroke (just over half the correct 1.45cc delivery).

I tried adjusting it and found the first strange/frustrating issue - the pump linkage on this EMPI carb fouls on the carb body when the adjuster is set to around 3/4 of max (pics below), so the throttle lever does not return to 'rest'. At that point, it delivers around 1.10 - 1.20cc/stroke (I used ten strokes, measured the volume with syringe and divided the result by ten. I refilled the carb after each test.).

I decided to compare it with a Solex 34 PICT-3 that I used for a few years until I stripped the idle solenoid thread (recurring sticky solenoid problem). At its max position; the linkage on the Solex clears its carb body, but the Solex's pump only delivers 1.15cc/stroke at that max position.

So; neither carb delivers 1.45cc/stroke. The EMPI may be able to at 'max', but the linkage fouls the body before that. I could try swapping the Solex pump linkage on to the EMPI, but the Solex doesn't seem able to deliver 1.45cc either.

I don't have a reliable 'before and after' benchmark because I rebuilt the engine to stock configuration. It always had a bogging issue, but before the rebuild it had a Engle 110 cam in that was strangled by the single carb, so I'd assumed that the cam was part of the issue. It now has a stock cam and the bogging issue is still there.

Questions:-

How likely is it that the shortfall in pump volume is causing the bogging issue? Even at minimum setting it squirts as soon as the pedal is pushed, but obviously isn't delivering the full specified volume at mimimum.

Is it worth trying to swap the accelerator pump over from the broken Solex? The EMPI linkage currently fouls 'at rest' with the adjustment set to 3/4, but the Solex unit doesn't seem to deliver the full 1.45cc/stroke even with full trave.



Solex on the left, EMPI on the right. EMPI is at 3/4 adjustment and the linkage fouls the carb body...

Image may have been reduced in size. Click image to view fullscreen.


Contact point between the EMPI linkage and carb body at 3/4 of max setting...

Image may have been reduced in size. Click image to view fullscreen.


Position of the EMPI throttle lever when the pump linkage fouls on the body at 3/4 adjustment (cannot return to rest)...

Image may have been reduced in size. Click image to view fullscreen.


Solex linkage clear of the carb body at max setting...

Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Mon Apr 12, 2021 10:30 am    Post subject: Re: Another bogging/lugging problem Reply with quote

Just out of curiosity, maybe I missed it, but WHY are you using some aftermarket p.o.s. when you have a REAL Solex at hand?

If it's really a carb-related issue, I expect it is more of a problem in the transition ports/fuel/pressure than the accelerator pump.
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PostPosted: Mon Apr 12, 2021 12:16 pm    Post subject: Re: Another bogging/lugging problem Reply with quote

FreeBug wrote:
Just out of curiosity, maybe I missed it, but WHY are you using some aftermarket p.o.s. when you have a REAL Solex at hand?


I mentioned it above. The threads that the cut off solenoid screws in to are stripped. It's scrap.
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PostPosted: Mon Apr 12, 2021 12:33 pm    Post subject: Re: Another bogging/lugging problem Reply with quote

I would be tempted to try re-bending the accelerator pump linkage on the EMPI to match the Solex - flatten it out, measure and re-fold in the correct position.
Then use the Solex accelerator pump linkage on the EMPI when that approach fails..

Or drill out the damaged thread on the Solex and JB weld a working shutoff valve into the hole.

Or drill out the thread, and get a piece of brass tubing you could tap with the thread for the shutoff valve, glue that in place with JB Weld.

It may not be quite as scrap as you think.


I noticed on a couple of occasions with the 34PICT-3 on a bus engine that it hesitated less if you adjusted the air volume and mixture screws for the correct idle, then opened up the mixture screw a fraction.

Also I dont know if your split screen era oil bath air cleaner has the hot air feed from the No2 head - as that also makes quite a difference on cold days to the way the engine picks up.
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PostPosted: Mon Apr 12, 2021 1:06 pm    Post subject: Re: Another bogging/lugging problem Reply with quote

mikedjames wrote:
I would be tempted to try re-bending the accelerator pump linkage on the EMPI to match the Solex - flatten it out, measure and re-fold in the correct position.
Then use the Solex accelerator pump linkage on the EMPI when that approach fails..

Or drill out the damaged thread on the Solex and JB weld a working shutoff valve into the hole.

Or drill out the thread, and get a piece of brass tubing you could tap with the thread for the shutoff valve, glue that in place with JB Weld.

It may not be quite as scrap as you think.


I noticed on a couple of occasions with the 34PICT-3 on a bus engine that it hesitated less if you adjusted the air volume and mixture screws for the correct idle, then opened up the mixture screw a fraction.

Also I dont know if your split screen era oil bath air cleaner has the hot air feed from the No2 head - as that also makes quite a difference on cold days to the way the engine picks up.


I've considered thread repair compound, I don't think there's enough metal on the casting to cut new threads or insert a bush and cut threads in that. I've not bothered because EMPI carb has been as good as the Solex ever was (better if you consider that the idle cut off has never stuck on me).

I've ordered a gasket set and will have a go at the acellerator pump/linkage while the carb is off. If that doesn't improve things, I'll try some of the other suggestions. (And yes, the air cleaner has a warm air pickup).


A lot of the stuff I've found about bogging down recommends checking the accelerator pump, which I why I'm focussed on that right now.

What I'm still not sure of is to what extent the volume that the pump discharges affects acceleration.

I can feel the engine start to react when I hit the pedal, which suggests that the pump starts to discharge quickly enough, but it doesn't carry on and pick up from there.

Is that simply because it's not discharging enough volume to sustain that initial pickup long enough to draw in enough air to start pulling more fuel in through the jets?
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PostPosted: Mon Apr 12, 2021 6:56 pm    Post subject: Re: Another bogging/lugging problem Reply with quote

I’d work on getting the linkage set so that it doesn’t bind. You may be able to try installing to Solex pump jet in the Empi carb to see if that makes any difference in volume once the linkage issue is resolved.
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PostPosted: Wed Apr 14, 2021 9:52 am    Post subject: Re: Another bogging/lugging problem Reply with quote

Clean your points and try again. Also yank a plug wire at dist while idling and if you don't see a nice blue/white spark and hear "CRAACK" on every firing pulse you may have a weak ignition.

Then mess with the carb. I run an Empi carb on my car (and have for a few years now) and they work fine. Better than most Solexes that have gone through my hands now Rolling Eyes


Also, if you really want to know if it is underfueling, unseat the idle jet by about a 1/4 turn and go for a test drive (short, as it will be loose and may fall) all better? Then get a bigger idle jet.

Sometimes the idle jets get overtorqued and they do all sorts of strange underfueling behavior. I have "hacked" my way into not throwing a carb away by putting a small "slit" in a JUNK IDLE JET tip with a razor blade. This allows some more fuel in but what it will do in transition from idle to main is anybody's guess... Motor running with this (friend's buggy) is doing just fine and plugs look ok but maybe this crap alcohol infused gas we get here plays in my favor.


Always adjust idle mix when making a change.


Good luck.

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PostPosted: Sat Apr 17, 2021 11:27 am    Post subject: Re: Another bogging/lugging problem Reply with quote

Frank Bassman wrote:
Clean your points and try again. Also yank a plug wire at dist while idling and if you don't see a nice blue/white spark and hear "CRAACK" on every firing pulse you may have a weak ignition.


I had a couple of hours free this afternoon and pulled the plugs. They were all sooty, so it must be running rich.

Plugs 3 & 4 were also wet with fuel. 3 particularly. Not sure if that's a symptom, or just fuel discharged from the last test with the carb in the car that drained down to the 3/4 side.

I cleaned the plugs and checked for spark by turning the engine past the firing point with a spanner on the crank and the ignition on.

I wouldn't describe the spark on any plug as a 'CRAACK'. More of a 'tick'. The spark on each plug was mostly blue.

I checked the leads with a spark tester (the type with two electrodes and a gap so you can see the spark jump https://www.lasertools.co.uk/product/5655/Adjustable-Spark-Tester).

I got a weird results with that tester though. Every time I turned the crank past the firing point, I could hear a click as the points closed, but I didn't always get a corresponding spark at the tester. When it did spark, the spark was thin, but blue. I had the tester gap set to the bottom end of the range prescribed for a standard single spark, single coil ignition. I had the same condition on each lead.

I'm not sure whether the intermittent spark with the tester is because I was turning the crank by hand rather than cranking it with the starter? I can't see why it would though. The plugs sparked every time the points closed when I tested them in that way. The purpose of the tester is to simulate the spark condition in the cylinder rather than in air.

I checked the coil resistance. Both sets of windings were within specs (primary 3.8 Ohms, secondary 9,000 Ohms).

The points are clean. No pitting or peaks.

The battery is good (I keep it on a battery conditioner).

I'm confused why it would only spark intermittently when I used the tester?
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