TheSamba.com :: View topic - Strange Idle Problem

Fri Aug 29, 2008 6:34 am

I've got a strange idle problem on my 1600 dp. It's a rebuilt motor and basically, it won't idle when the choke plate opens. It falls dead on it's face as if you turned the key off. I've got an H30/31 carb newly rebuilt and a 009 distributor. I've checked the idle shut off solenoid, pulled it out and verified it does move in and out, switched the carb out with a 34 PICT 3, same problem, double checked the manifold boots, triple checked all vac ports are closed off, double checked valve adjustment, changed points, condenser and rotor, gapped points, checked plugs, gap is correct and they are not sooty, checked the float level in the carb, took both carbs apart and blew them out, and still no idle. The next thing I'm going to do is check the manifold pressure, this may tell me if there is a vac leak. Can someone tell me what the correct pressure should be? Anybody see anything I've missed? I also need to check the seal between the manifold and head. I'm pulling my hair out here!
Greg

Fri Aug 29, 2008 7:11 am

Ouch, that is pretty weird. It would probably have to be a pretty bad vacuum leak for such a bad idle problem. You could do a quick check for that by letting it idle while it's choked and before it falls on its butt by doing the spray ether starting fluid at your manifold flanges and boots and seeing if the engine speed spikes or dips.

You said new build on the engine, how's the compression? How does it run at higher engine speeds? Firing order is correct right? And well does the 009 advance and then come back off the advance with the engine revs? You have it timed to around 8-10 BTDC statically right?

If you happen to have an old idle cutoff valve you don't mind mangling you might try just cutting off its plunger and putting that on your carb to totally eliminate that as a possibility. And specficically double check the pilot jet again and see if its clear.

That's about all I can think of to look at right now..

-Andy

Fri Aug 29, 2008 7:37 am

I haven't checked the compression, that's on my list. I tried spraying it, only thing I had was carb cleaner though. Didn't make a difference. I also tried the plunger trick. Had an old one laying around that had already been cut, still no difference. Still wants to die at higher revs, I've cranked the fast idle screw up and moved the timing all around but it makes no difference. Also, I can blip the throttle lever and it will run ok for a few seconds and then dies, kinda like it's running on the fuel from the accelerator pump and then runs out. It is timed statically around 8, but I've moved it all over trying to find somewhere it will idle. Firing order is correct; 1-4-3-2. I will look at the jets again. I'm running a 132 main which should be plenty on a 34 PICT or an H30/31, even with a 009.

Fri Aug 29, 2008 8:12 am

I'm not sure what else to say now. Except, you checked for a good strong spark coming out of the coil right? And that a 132 might be over-large for an H30. Otherwise, sounds to me like it should run. Fresh build right? Hopefully nothing awful like getting the timing gears in there off by a tooth occured.

Fri Aug 29, 2008 8:57 am

Check the idle pilot jets for blockage and see this for the "overtightened jet syndrome" Most common on 34 pict 3 but can be a factor on other models too.

Rarely have I seen it on the H 30 31 but I have a few times.

Try the "sweet spot" approach I describe in this thread.

http://www.thesamba.com/vw/forum/viewtopic.php?t=56411&highlight=idle

Also 132 main is a bit rich IMHO for the H 30/31 but that is not the cause of this particular problem.

Also make sure you have the smaller of the two pilot jets in the side of the H 30/31 and the larger in the angled one. Generally they are 45 or 50 in side and 65 in the angle port.

Fri Aug 29, 2008 12:58 pm

glutamodo wrote: I'm not sure what else to say now. Except, you checked for a good strong spark coming out of the coil right? And that a 132 might be over-large for an H30. Otherwise, sounds to me like it should run. Fresh build right? Hopefully nothing awful like getting the timing gears in there off by a tooth occured.

Good spark. It's sort of a fresh build. I rebuilt it about about 10 years ago and never used it. Before I put it in I pulled the cylinders apart and replaced the cylinders, they were rusted and pitted. Everything else looked good. I didn't think it would run at all if it was a tooth off on the timing.

keifernet wrote: Check the idle pilot jets for blockage and see this for the "overtightened jet syndrome" Most common on 34 pict 3 but can be a factor on other models too.

Rarely have I seen it on the H 30 31 but I have a few times.

Try the "sweet spot" approach I describe in this thread.

http://www.thesamba.com/vw/forum/viewtopic.php?t=56411&highlight=idle

Also 132 main is a bit rich IMHO for the H 30/31 but that is not the cause of this particular problem.

Also make sure you have the smaller of the two pilot jets in the side of the H 30/31 and the larger in the angled one. Generally they are 45 or 50 in side and 65 in the angle port.

I will check these tonight. I'm pretty sure there were 2 50's in both the straight and angled ports. Could this be my problem?

Fri Aug 29, 2008 6:04 pm

When it dies open the top of the carb and see if there's any gas in the float bowl. Maybe your fuel pump's bad?
Are all the vac hoses hooked up correctly?

Fri Aug 29, 2008 7:29 pm

mnussbau wrote: When it dies open the top of the carb and see if there's
any gas in the float bowl. Maybe your fuel pump's bad?
Are all the vac hoses hooked up correctly?

Carb's full. All the hoses are plugged.

Fri Aug 29, 2008 9:50 pm

And since you changed carbs, you'd know if the other one wasn't full as well, so I won't ask that one... This is just plain weird. How well does it run at speed?

-Andy

Sat Aug 30, 2008 2:40 am

glutamodo wrote: And since you changed carbs, you'd know if the other one wasn't full as well, so I won't ask that one... This is just plain weird. How well does it run at speed?

-Andy

I haven't had it out on the road to see. But it runs ok around the yard as long as the choke is at least half closed. One thing I've noticed is if I turn the motor by hand I hear a gurgling sound as the compression leaks off on #3 and 4, I haven't checked compression yet but could compression issues cause something like this? Maybe that would cause there to be low vacuum in the manifold which would'nt pull enough fuel from the carb. I think I read that there should be 15 lbs of vacuum at idle, is this correct? I'm grasping at straws now!

Sat Aug 30, 2008 5:15 am

I'm no expert but Tom Wilson's "Rebuild Your VW Engine" book says 10 in. while cranking. Warm up the engine, shut if off, pull off the coil-to-distributor wire so it won't start. Connect your vacuum gage to a full manifold vacuum source -- off the manifold, not the carb. Crank the engine and note the vacuum. The needle might swing up to 2 in. If it drops regularly to 0, you might have improperly adjusted or burned valves, worn cam lobes, pulled head studs, warped heads or cylinders, pistons, or rings.

The vacuum will drop about 1 in. for each 1000 feet increase in altitude, from sea level.

Sat Aug 30, 2008 6:28 am

I am having idle problems also, checked the valve and found it did not work. I just purchased a new idle bypass valve (part # 049129412C) but it is different than the one on the carb. Are these interchangeable?
Thanks for any info!

Sat Aug 30, 2008 7:48 am

mnussbau wrote: I'm no expert but Tom Wilson's "Rebuild Your VW Engine" book says 10 in. while cranking. Warm up the engine, shut if off, pull off the coil-to-distributor wire so it won't start. Connect your vacuum gage to a full manifold vacuum source -- off the manifold, not the carb. Crank the engine and note the vacuum. The needle might swing up to 2 in. If it drops regularly to 0, you might have improperly adjusted or burned valves, worn cam lobes, pulled head studs, warped heads or cylinders, pistons, or rings.

The vacuum will drop about 1 in. for each 1000 feet increase in altitude, from sea level.

Does it matter if the choke is closed or not?

Sat Aug 30, 2008 8:21 am

Larry's 62 wrote: I just purchased a new idle bypass valve (part # 049129412C) but it is different than the one on the carb. Are these interchangeable?

You mean like this as in different?

If they both have the same threads and have a plunger on the end of them, yes they are interchangable. Original ones had a large body, replacement ones, depending on who made them, either have a large body or a smaller body. I don't know if one style works better than the other, the smaller one, being lighter, might put less stress on the threads in the carb body though, over time.

Now, if they sent you a pilot jet type idle cutoff valve...

it won't replace a plunger type cutoff valve. However, it will function in a plunger type carb, I don't think I've ever seen a H30 or 34PICT-3 carb that had one on it but, actually the pilot jet type should work to kill the idle, if it's 12V - as it works on any Solex carb with a pilot (idle) jet on the right side. But you'd have to either have the other valve working as well or cut the plunger off of it.

-Andy

Sat Aug 30, 2008 8:39 am

gregthomas wrote: Does it matter if the choke is closed or not?
Wilson says to warm up the engine, so I'd say the choke plate should be fully open.

Sat Aug 30, 2008 8:59 am

Yes like that as in different. The threads are the same. Thanks for the quick reply.

Sat Aug 30, 2008 9:16 am

mnussbau wrote: gregthomas wrote: Does it matter if the choke is closed or not?
Wilson says to warm up the engine, so I'd say the choke plate should be fully open.

Ok, I'm out of town today, I'll try these things tomorrow and let you guys know. Thanks for all your help!

Wed Sep 03, 2008 6:10 pm

I haven't had a chance to check the compression or vacuum yet, but I did pull the carb back apart again, and all the jets are open, and the pump is sending plenty of fuel. Here's a video of it crapping out. This is after the engine has warmed up for about 5 minutes, and I've set the choke so it doesn't open all the way. When I manually open the choke, it falls on it's face.

http://www.itookthisonmyphone.com/gregthomas/mediab9fe8efb0b6944b5852270c95d304fa7

Wed Sep 03, 2008 8:55 pm

gregthomas wrote: I haven't had a chance to check the compression or vacuum yet, but I did pull the carb back apart again, and all the jets are open, and the pump is sending plenty of fuel. Here's a video of it crapping out. This is after the engine has warmed up for about 5 minutes, and I've set the choke so it doesn't open all the way. When I manually open the choke, it falls on it's face.

http://www.itookthisonmyphone.com/gregthomas/mediab9fe8efb0b6944b5852270c95d304fa7

Besides checking to see it the pilot jets were 'clear' did you try the "sweet spot" deal on the one straight in the side ? I linked you to a thread about it?

I can't tell shit from that video... sorry... but I do believe you! :P :lol: :wink:

Sat Sep 06, 2008 9:34 pm

Update - I double checked my valve adjustment, all was good. Also checked the vacuum, it pulses from 10 to 0 in. Not good. I also checked the compression:
1 - 100
2 - 100
3 - 95
4 - 120

This seems bad, like I've pulled a stud out of the case, or the head needs to be re-torqued. Will these issues cause it to not idle with the choke open? I'm going to pull the motor and check it out. Will a burned valve be obvious when I pull the head off? These are used heads so I'm leaning toward a valve problem.