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no power above 2k and backfiring

FM Former Member
Hi guys. I need a little help here. I'm enjoying my Roadster, but all my engine experience is with small block chevys. I figure an engine is an engine, but then again, these air cooleds are a different breed. I figure it's better to ask those with the experience and head down the right road than to mess around and waste time.

The car was running excellent. Pulling and reving well. Then last night I was out for a drive, and the engine would begin to run rough above 2000 rpm, and had no power at all. If I lift my foot just a bit, it runs smoothly, but won't gain any rpm. If I give it a bit more gas, it runs rough. Also, it backfires even with the throttle on. It will accelerate from a stop light, up to 2000 rpm with out a problem, but the minute I stop accelerating and hold a cruising speed, it starts to backfire a bit. During deceleration it backfires it bit too, but not at idle. It runs a bit rough at idle, but it always has.

I'm thinking carbs or timing advance. I'm not familiar with dels, but have ordered the manual. Until I get it, can someone tell me where on the carb to check? Any other ideas?

Thanks for your help.
Ron
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FM Former Member
Hi guys. I need a little help here. I'm enjoying my Roadster, but all my engine experience is with small block chevys. I figure an engine is an engine, but then again, these air cooleds are a different breed. I figure it's better to ask those with the experience and head down the right road than to mess around and waste time.

The car was running excellent. Pulling and reving well. Then last night I was out for a drive, and the engine would begin to run rough above 2000 rpm, and had no power at all. If I lift my foot just a bit, it runs smoothly, but won't gain any rpm. If I give it a bit more gas, it runs rough. Also, it backfires even with the throttle on. It will accelerate from a stop light, up to 2000 rpm with out a problem, but the minute I stop accelerating and hold a cruising speed, it starts to backfire a bit. During deceleration it backfires it bit too, but not at idle. It runs a bit rough at idle, but it always has.

I'm thinking carbs or timing advance. I'm not familiar with dels, but have ordered the manual. Until I get it, can someone tell me where on the carb to check? Any other ideas?

Thanks for your help.
Ron
FM Former Member
It would be helpful to know which carburetor(s) and fuel pump your car has because my chrystal ball is in the shop for repairs. If Weber IDF's I would check for fuel delivery and pressure (3.0 to 3.5 psi downstream of the pump), plugged main jet, stuck float. If you can't get past transition you are either too lean (something plugged) or too rich (maind jet stack loose, float stuck open, or too much fuel pressure). Also check to make sure your ignition advance isn't stuck closed and timing hasn't slipped.
(Message Edited 7/11/2003 2:09:35 PM)
FM Former Member
The car is a 1992 IM with the 2085 engine. The carbs are dellortos. (44's?) Don't know what fuel pump.

I am checking the timing, but my guess would be carbs because of how it runs below 2k, though you are right, if the timing isn't advancing that would do it.

I haven't checked the plugs yet to see if it is too rich or lean, but I was thinking lean because it was running hotter than normal. Is that right?
FM Former Member
This will sound simplistic, but..... well it happened to me. Same symtoms, and I automatically started thinking trash in the carbs, yada. But like may pop taught me I went to trouble shooting 101 basics and started the routine checks to isolate whether it was an ignition or fuel problem. Right in the middle of step one I was checking plag wires, reached back to #2 and found that I had been either sloppy on my last tune-up or I had a bad cap on the wire, because there it was, plain as all get out... #2 plug wire laying on the tin, unconnected.

Moral of story... just like on a SBC, you trouble shoot with the old time basics, Fire or Fuel? Isolate then go to step 2.

Jim
Dub-U-Tub
FM Former Member
Jim, Good thought, and that is one of the first things I checked. I pulled all the plug and distributor wires and reattached to make sure they are making good contact. I will check them again just to make sure.

Ron, I have checked the distributor, and will check again. It is not a vacuum advance dist. (009).

Last night when I was driving, with the engine behind you it is hard to hear exactly what is going on. Today I am finding that it is even backfiring at idle. I will check for an exhaust leak next.

Thanks for the ideas guys.
More ideas?
FM Former Member
The distributor is advancing. Timing is correct (that is if 32deg at 2800 is right). All cylinders are firing. It's not backfiring at idle any more, but still backfires when the revs are up, and stumbles/hesitates, with no power. It feels like it is running out of fuel because of the way it responds when I lift off the gas (it runs better), but being rich could have the same result couldn't it? How do I tell/check this? I guess the backfiring indicates it is rich. How do I dial down the mixture?


(Message Edited 7/11/2003 5:28:31 PM)
FM Former Member
I just noticed another thing. I just had the car idling for about 15 minutes and I noticed the exhaust was only barely warm. Not sure if this is right or not, but it got me to checking the temps of engine parts and I then noticed that the left (drive side) intake manifold is very hot. Too hot to touch for more than a second. The right side intake manifold is only barely warm. I'm assuming that is from one or both cylinders on the left side running hot? A sign of too rich an idle mixture?
(Message Edited 7/12/2003 1:17:17 AM)
FM Former Member
Well, the carbs seem fine. The only thing I haven't checked is to see if the floats are sticking. After reading a few of your comments, and a few other posts, I am now starting to think ignition system. I will change all the plug wires tomorrow and see if that helps. What else should I try? Is changing to electronic ignition a good idea? I have read some good things about the Pertronix II ignition and coil. Is that a good way to go?
FM Former Member
George says the Pertronix set up is primo. I have a CompU-Fire and enjoy good results with it. I did fry the transistor on one somehow, someway, but had (on the advice of forum sages) kept all the point hardware in my ER Road kit. Now, I just keep a spare 009 with the Comp-UFire in it. Haven't needed it, but it's there with my spare cables, fuel lines, plugs, etc...

Anyway, the starts are crisp, great idle, smooth all through the revs, anddddddddddd NO POINTS.

Jim Ward
FM Former Member
I have now installed a new distributor, including Pertronix II electronic ignition, and a Pertronix II coil, new wires, and new plugs. Timing is set to 10 deg at idle which works out to about 30 deg at full advance.

When I drive the car it drives fine, till I get to a hill or step on the gas hard. Then it kind of 'bogs' down, and 'clatters', and slows down. If I back off the gas, it smooths out. I can make it up a hill by feathering the throttle.

Does this sound familiar to anyone? What else should I be trying to find the problem? Also, where should I focus my efforts, timing or carb?

Ron

(Message Edited 7/16/2003 2:10:59 AM)
FM Former Member
George, if the car was running fine for the first week I had it, and then suddenly developed this problem, could it still be caused by running too lean? I will try retarding the timing today as that is the easiest thing to try. As for jetting, is it the main jets that I would try making larger? One size? (140s to 150s?)
Thanks, Ron
FM Former Member
"Too lean" can also be caused by a small piece of crud partially blocking a carburetor jet or passage in a carburetor or a float sticking closed. If the problem has not always existed but occurred suddenly check out the carbs.

Also the carbs may be starved for fuel; check both fuel pressure (3.0 to 3.5 ps1) and supply (tank vent plugged, internal tank filter or fuel line blocked with crud).
FM Former Member
I have checked the timing all the way from 5 to 15 at idle, and it's about the same. I have found I can 'power through' the dead spot in first and second, but not third where it just bogs.

George, I don't have a fuel pressure gauge. I did try running the pump into a glass, and get about an ounce of fuel in about 2 seconds of cranking with the starter motor. Does that tell you anything?

Also, I have checked the jets a number of times and they always look good. I have not checked the floats yet, but did check one of the accelerator pumps and it was clean.

George, how do I check the tank vent? The car is a 1992 IM.
Thanks.
FM Former Member
Any NAPA or other auto supply store should have a relatively inexpensive fuel pressure gauge. You simply remove the line to the carbs and either attach the gauge to the pump outlet directly or "T" it into the fuel line with some extra fuel line and clamps.

There should be a small vent hose running from the gas tank filler neck down to exit near the bottom of the chassis; it may have a check valve in it. If it isn't clear or the check valve is stuck (or installed backwards) it can either impede flow (form a low pressure area in the empty tank area) or pressurize the tank (force fuel through/past the pump at higher than normal pressures). Which happens depends on the amount of fuel in the tank, ambient temperature, slosh in the tank, etc.

Stock VW fuel tanks usually have an internal filter; when the fuel level is low you can look through the filler neck with a flashlight (don't use a match, ha ha)and see if there is crud in the fuel and filter. If so you may need to have the tank cleaned and sealed 9or do it yourself).
FM Former Member
I picked up a fuel pressure gauge today. 2psi is what I get. George you were saying the pump should produce 3 to 3.5 psi so I guess I need a new fuel pump. Any chance the low fuel pressure could be caused by crap in the lines or filters somewhere?

I currently have a mechanical fuel pump. Is that pretty standard or is there value in switching to an electric pump?
(Message Edited 7/17/2003 12:53:57 AM)
Ron ORon O1984/2010 IM, B.C. Canada
Ron, getting the fuel lines as far away from the motor as possible is a good thing. Check out the picture of my engine compartment. I've got the fuel line coming out of the firewall, through a regulator and then to my dual Webers. Steel lines were not necessary, but I though they looked cool.





FM Former Member
Nice looking engine set-up Ron! To run that set-up, you are obviously running an electric fuel pump. Where is it located? What is it wired to?

My fuel pump is mechanical and therefore is on the engine. I made the assumption there is only the one pump. Is that correct? Does it matter if the fuel is pulled at the engine or pushed from the tank?

Still looking for opinions on electric vs mechanical. Is electric the prefered way to go?

I have seen an electric fuel pump on CIP web site, but it says 2.5 to 3 psi (20 gallons/hour). George you say 3 to 3.5. Is 2.5-3 enough pressure George?
Ron ORon O1984/2010 IM, B.C. Canada
Yes, I'm running an electric fuel pump. It is located up front, just above the steering components. I can't remember the brand of the pump. I installed good fuel filters before and after the pump and also installed a cut-out switch (for anti-theft). I agree with George, that you need a fuel pump that puts out 3 to 3.5 pressure. I installed the fuel regulator as a precaution.
Ron
FM Former Member
Ron, the stock fuel pump output pressure is adjustable. There is a pushrod, and you can increase its stroke by using a thinner gasket/spacer setup between the pump and engine case (increase the effective operating stroke length). A Bentely VW shop manual will describe this procedure.

Assuming the pushrod is not excessively worn (or the wrong one - there are two lengths) you should be able to adjust the pressure up to 3.0 to 3.5 psi - assuming that the pump itself is OK. A stock VW fuel pump should work fine for most normally aspirated performance engines up to 2,276cc.

CB Performance has rotary (quieter) 12V electric fuel pumps with built in 3.5 psi regulation.
(Message Edited 7/17/2003 2:35:52 PM)
FM Former Member
Thanks George. I understand what you are saying about how to adjust the pressure. There is a 1/2" spacer under mine now. I am thinking I am going to chance to an electric pump, but in the mean time, I will try to get a shorter spacer. Any recommendation how much smaller a spacer I need? Ron
(Message Edited 7/17/2003 2:46:46 PM)
FM Former Member
I just got back from my test drive after installing the electric fuel pump. YAHOOOO! It's now running better than ever. Of course tomorrow I have to reset the carbs as it is now running rich, but rich is better than lean any day!

Thanks guys for your help and ideas, especially George, you were right on with the fuel pressure diagnosis. If you hadn't pushed me to go get a fuel pressure guage, I'd still be fighting this gremlin.

Ron
(Message Edited 7/22/2003 1:25:46 AM)
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