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28 PCI Disassembly/Running Issues
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rayvwbug
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PostPosted: Sat Sep 18, 2010 1:37 pm    Post subject: 28 PCI Disassembly/Running Issues Reply with quote

I am trying to resolve a problem with a 28PCI. I have had this apart several times now, but even though idling, etc is now good, it will not accelerate correctly and acts lean under load. Couple of questions:
1. This carb does not have a venturi retaining screw anywhere that I can see. How is it held in?
2. Saw in other posts about cleaning the small accelerating holes that are just above the vacuum port. While I can confirm they are open in the carb throat, where do they get fuel from- where can I blow through to confirm they are open all the way to the fuel source?

Carb idles perfectly, starts easily, and I can pull out in first ok, but it just spits and sputters after shifting into higher gears. Checked points/dwell, timing, valves, and plugs, so am concentrating on the carb. Any other ideas?
Thanks

Ray
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Snort
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PostPosted: Sat Sep 18, 2010 4:06 pm    Post subject: Reply with quote

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I would recommend having your distributor professionally serviced as well. Springs get worn, diaphragms begin to fail, without a machine to test the curve you will only be guessing about its' true condition.
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PostPosted: Sat Sep 18, 2010 6:18 pm    Post subject: Re: 28 PCI Disassembly/Running Issues Reply with quote

RoboRay wrote:
I am trying to resolve a problem with a 28PCI. I have had this apart several times now, but even though idling, etc is now good, it will not accelerate correctly and acts lean under load. Couple of questions:
1. This carb does not have a venturi retaining screw anywhere that I can see. How is it held in?

Thanks

Ray


Choke is held in by the screw which is left of the upper left screw that holds the accellerator pump diaphram on..Maybe yours is different?

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rayvwbug
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PostPosted: Sat Sep 18, 2010 7:58 pm    Post subject: Reply with quote

Yup, mine is different- there is no screw that holds the venturi. I gave up and put the carb back together. I was able to confirm the accelerator drillings in the carb throat were open to the pilot jet and saw no need to remove the venturi.
Anyone have a good place to send a distributor to be gone over? Watching with the timing light earlier I could see it advancing. Not sure how to check centrifugal vs vacuum advance though other than simply disconnecting the vacuum and watching to see if I still get advance?
Thanks
Ray
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PostPosted: Sat Sep 18, 2010 10:53 pm    Post subject: Reply with quote

Does it rev up fine when you have it sitting idling in your driveway?

If it's off and you pump the accelerator, do you see gas shoot out? No would be a the accelerator pump is not working or those passageways are plugged.

Sometimes the little ball bearing in the passage way gets stuck over the years and prevents acceleration. You can see it in the diagram above on the right hand side.
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rayvwbug
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PostPosted: Sun Sep 19, 2010 6:25 am    Post subject: Reply with quote

It will rev fine in the driveway once reasonably warm. I had both the larger and smaller ball out yesterday and they were in very clean shape- acc. pump is working. Any idea what holds the venturi in?

Thanks
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Barry L. B.
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PostPosted: Sun Sep 19, 2010 6:51 am    Post subject: Reply with quote

RoboRay wrote:
Yup, mine is different- there is no screw that holds the venturi. I gave up and put the carb back together. I was able to confirm the accelerator drillings in the carb throat were open to the pilot jet and saw no need to remove the venturi.
Anyone have a good place to send a distributor to be gone over? Watching with the timing light earlier I could see it advancing. Not sure how to check centrifugal vs vacuum advance though other than simply disconnecting the vacuum and watching to see if I still get advance?
Thanks
Ray
Ray,my 56 acts similar but I couldn't accelerate without giving some choke and after testing the distributor I found the vac. advance wasn't working at all and if it could there was hardly any advance in the dist. by moving with a screwdriver so I put on a new 009, plugged the vac. port in the carb., timed it retarded then painted a white area 1.85" to the right of the notch on the crank pulley. At high rpm using a strobe timing light the advance moves to the r.h. end of the white area. After she warms up I don't get the bogging down when I put it in high at 45. Barry
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Motorhead55
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PostPosted: Sun Sep 19, 2010 12:17 pm    Post subject: Reply with quote

You can chect the dist diaphgram two ways. Disconnect it at the carb and use a vacuum pump with a gauge or do it the cave man way (the way I do it!) and suck with your mouth and see if it holds. If it leaks off suction then it is bad. The other way is with a timing light. Check with everything hooked up and bring the rpm up to about 2500 rpm while looking at the timing mark's orientation running and see how far it looks at "full advance" Next disconnect the vacuum line at the dist or carb and plug it so it won't leak to the carb. Repeat the timing check and see if it is any different. I have an old Craftsman timing light with a degree wheel on it. I run up the rpm and adjust the wheel until the timing mark is at the case split. I read the amount of advance at the timing light.
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rayvwbug
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PostPosted: Mon Sep 20, 2010 9:19 am    Post subject: Reply with quote

These are great ideas to test vacuum advance, etc. I also have the old Craftsman light like you are describing. I drove the car yesterday and it seems it is now down to just a transitional issue between idle and open throttle. The warmer the engine got the better it ran. It will still bog for a short time initially after shifting(sometimes pops, seems lean), but runs quite well at a more open throttle. Noticed a fairly large temperature difference between the two sides of the heat riser- perhaps it is blocked. One side I could not touch, the other was warm. Intake was fairly warm to the touch so I would think it would not be the cause of the lean issue by the time it gets that warm? Been awhile since I have fought the single carb woes!
Thanks All
Ray
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rayvwbug
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PostPosted: Mon Sep 20, 2010 5:18 pm    Post subject: Reply with quote

Anyone know what total advance should be? I assume centrifugal comes in first, then vacuum adjusts the timing based on changes in engine load? Any idea on how much advance each should provide?

Thanks!
Ray
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rayvwbug
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PostPosted: Mon Sep 20, 2010 6:59 pm    Post subject: Reply with quote

Or do I have that advance scenario backwards??
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rayvwbug
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PostPosted: Sat Oct 09, 2010 5:43 pm    Post subject: 28 PCI Disassembly/Running Issues- Now 36hp Rebuild? Reply with quote

So today I completed replacement of the intake manifold. Replaced all the gaskets, crush rings, etc. This did not change the stumbling symptoms at all. Heat riser is definitely open. I also tested vac advance- does not leak and it moves the advance plate. Twisted rotor and advance snaps it back. I am at a loss as to what is at the root of this stumbling badly after shifting, in fact it just sputters within a certain rpm range.
I replaced the manifold in the car by raising the fan housing a bit and took the fan off the front of the generator. What I was able to see while the fan was out is a very thick layer of grime, even to the point that the fins in the oil cooler and the 1/2 cyls are caked with this such that there can be no air getting through. Think it is time to drop the motor and rebuild. This is the original motor, so I want to try to reuse it. There is very little end play so I think the case is usable. So.. where do I get 36hp rebuild parts and who will machine a 36hp case that is very important to me?

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Ray
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Flavio
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PostPosted: Sun Oct 10, 2010 1:57 am    Post subject: Reply with quote

You could try just to remove the Air Jet (I think the stock one is a 198) and put there a smaller one, like a 180 or 170. Do not tigth this jet or you can broke the top of the tube where it fits, just a very very small snug !
Reducing that jet the whole thing will run less lean. Try it.
Hope this helps
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my59
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PostPosted: Sun Oct 10, 2010 11:51 am    Post subject: Reply with quote

Before you wade into a rebuild, check compression, do a leak down test, and check oil pressure- it is very possible that the outside simply needs a good scrub and going over, not an internal rebuild.

I'd look into the fuel pump- if the internal valve springs are weak you may not be getting what you need under load.
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PostPosted: Mon Oct 11, 2010 9:44 am    Post subject: Reply with quote

I did rebuild the fuel pump. but had to use the original main spring as the one in the kit was much too thick and yielded 8psi of pressure. I had done a cold compression test recently and #3 was pretty low Readings were 110,96,87,106. Is it worth warming up to redo the test? Also thinking I am hearing a noise when accelerating that could be a rod knock.

Thanks
Ray
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my59
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PostPosted: Mon Oct 11, 2010 9:56 am    Post subject: Reply with quote

The manual says check compression with throttle open, all spark plugs removed, engine at operating temp, cranking over with the starter.

The tolerance spec is 100-121 psi (new parts), and the wear limit 64 psi.

I'd have another go at it.

When you re-did the fuel pump, are the interior valves thin little metal discs or the thick hexagonal fiber disks? I've found that the little metal ones do not seal as well as the hex ones.
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rayvwbug
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PostPosted: Mon Oct 11, 2010 10:07 am    Post subject: Reply with quote

I am almost certain I used the thicker ones- I just checked and the thin metal ones are in the box of parts I retained after rebuild, and have wear marks, so I am sure they are the ones I removed. As to just doing an external cleaning, the areas inside the valve covers were pretty sludged up as well. I will test oil pressure too. Thanks
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TomF
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PostPosted: Mon Oct 11, 2010 10:12 am    Post subject: Reply with quote

You can hook up a pressure gauge (like you would use with oxygen) to the outlet of the fuel pump and crank over the engine - that can give you an indication of what fuel pressure you're getting.
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rayvwbug
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PostPosted: Mon Oct 11, 2010 10:18 am    Post subject: Reply with quote

I did put a pressure gauge hookup in parallel with the carb while car was running. Think it was between 2 and 2.5psi
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PostPosted: Mon Oct 11, 2010 10:44 am    Post subject: Reply with quote

I have seen the housing crack around the base of where the air correction jet threads in and it leans the engine out and gives you A lean condition check for A crack in the air correction hosing where the red line is inside the red circle
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