Perplexing full throttle issue on 67S
 

I'll try to explain the problem as best I can, here are the basics though. The engine, a 2.0S with Webers, is fresh and runs very well(most of the time). Carbs adjusted, proper jets, proper float height (I set it on the high side of the PMO gauge), ignition seems good and uses a CDI box with a factory black coil.

Basically what happens is it seems to intermittently foul up the plugs for a few seconds, almost always when cornering, but sometimes when I just punch it. This is on regular curvy roads and especically autoX.

It will do this somewhere in the 3.5-4.5RPM range during the curve and coming out of the curve, then when I punch it, no go. I'll have to slip the clutch and blip the throttle a few times to "clear" it's throat and then it will rev again. During the period of bogging it acts like it's running on 3 cylinders or not getting any advance, it just won't rev and kind of sputters around under load.

If I run the engine up through the gears it goes without issue to redline in each gear, it only seems to be an issue if I punch it from somewhwere in mid revs.

The only thing I haven't done is check my accelerator pump volume's, could these be flooding the engine out if they were dumping too much fuel??

Help!
Bill

Have your webers been modified for adjustable accelerator pump volume? Not much to fiddle with if they haven't.

why do you think they are loading? black smoke? What do the plugs look like? Arguably you could be getting fuel sloshing away from the pickup port. Inside the float chamber there is a small divider at the bottom that is intended to prevent dirt from entering the carb. This little ridge will also prevent fuel from flowing under high-g conditions. Current mod is to use an end mill to remove this and epoxy in an aluminum dam to prevent. All covered in Bruce Anderson's book.

Are you sure the fuel tank is clean? Screen changed? What fuel pump, you aren't running an original Bendix are you?

Need more info on exactly what happens when it sputters.

What is your fuel pressure? Should be no higher than 3.5#'s or it will hesitate as described.

John, I'm aware of the float bowl mod, but I don't think that's it since it can do this in straight line acceleration sometimes.

Fuel pressure is 3psi on the guauge with a Holley regulator. It is a bendix pump, but I know it's working fine and these cars didn't run like this when new. I've also had a Facet in there and it ran the same.

I've put over 10K miles on it this way and plugs are always clean, and mileage is good.

I really have no idea what exactly is happening, I'm only guessing it's loading up rich. Like I said, it really runs great, especically if you run it up through the gears. It's just when I'm going into a corner part throttle and then gun it coming out. It sputters and I have to slip in the clutch and clear it's throat by blipping, and then off we go.

It's not just corners though. It will do this if I go to pass on a two lane. anytime I slam the throttle. If I gently ease into it and eventually achieve full throttle, it runs out great, but you've got to be very gentle, too much throttle at once and it bogs. No popping or backfiring, no black smoke. Just starts missing or feeling like I'm getting no advance but fuel is going in.

I thought my distributor weights were maybe sticking, but I've cleaned them up and they appear fine.


Here's the patient.

http://forums.pelicanparts.com/uploa...1201891005.jpg

As John suggests. Check the accelerator pump volume. The hesitation could be from a lack of sufficient fuel during sudden throttle opening. Air moves faster than fuel, thus the boost from a squirt under pressure.

With engine OFF, look into each carb. throat, then open the throttle. You should observe a squirt into the throat.

Hope this helps,
Sherwood

Yes, each throat gets a nice squirt. All look about the same. As far as I know these haven't been converted in any way, but you can adjust the linkage to the accelerator pump. Not sure what effect that has though.

The accelerator pumps need to be delivering a specific amount of fuel and that might be off. The S cars and the solex cam equipped cars do take a different driving approach they don't seem to like sudden throttle opening. The way I describe the weber IDA series of carbs is they are basically a switch they are either on or off....they don't have a very good quick transition. Not sure if this your problem but thought I would throw that in there

Yea, this is really excessive though, and I can't duplicate it in the garage. I've tried several times, holding it at 4K then flooring it to redline and it's smooth while under no load.

I need to take it out this weekend and get some more data points. It's been fairly random and I never worried much about it untill I did my first autox last season. It sputtered around the whole dang track since it was constant corners with on/off throttle.

"It sputtered around the whole dang track since it was constant corners with on/off throttle."

Only under load? Check fuel pump pressure and volume. You've described a symptom of a soon-to-fail pump.

There's an outside chance you're generating enough g-force to cause the fuel to centrifuge away from the fuel passage at the bottom of the float bowl. Thus, the Jerry Woods float bowl plate was born.

MHO,
Sherwood

I think the pump is ok since I can full throttle accelerate up through the gears for quite a while with no issues, so it doesn't seem like it's starving for fuel then.

The Jerry Woods mod is probably a good idea anyway, but I don't think that's my issue here, especically considering how slow I am, no way I'm generating enough G's.. :D

My thinking (which I doubt will wildly popular) is you have a case of Webers, S cams, & small displacement flat 6 woes. S cams don't really start to scavenge till
4500-5000K rpms. A rapid opening of the butterflies at 3500 (or thereabouts) that will cause your
intake charge speed to go to hell in a hand basket....the motor will go blaaa under load.

Being on this forum for some time has given me the opportunity (?) to read reports of a similar problem with this set-up even on larger engines. Seldom (if ever) have I seen any 2.0L s with this setup discussed here, but all one needs to do is read old car rag tests to find it. Most preferred the T or L for a daily driver due to the lack of tractability at part throttle. Frankly, I can't imagine how bad such a set up would be at an autocross where midrange is the cat's ass.

That said, I have set my floats just a skosh low to prevent flooding at autocross and they still have done it on a few occasions......on very rough corners.

BTW, I would invite for an AX pass anyone that thinks that Solex cams in a Webered 2.7L makes for an unresponsive throttle and I consider my tuning skills to be less than top notch.:D

What you describe is beyond any normal Weber "flat spot". I and many others have run stock 2.0S engines in autox events on the stickiest tires with no mods to the carbs (other than rejetting for modern fuel formulations) without such faults occuring. You need to isolate the problem a little better. Since you can't duplicate the problem in the garage or on the dyno in static testing, I would hook up a portable wide-band O2 sensor and drive around in the manner that makes it happen, while watching the A/F ratio display right when it occurs to see if you are going too rich or too lean suddenly. At least that would point you in the right direction and possibly eliminate half the guesses as to the cause.

I would not discount the possibility that it could also be an ignition fault, though.

Good luck,
TT

FWIW: I had a similar problem in that RPM range, although not quite as severe or consistent. After a year or 2 of screwing around, I pretty much pinned it on worn/leaking throttle shaft bushings because that was the only thing I could find wrong with the fuel system. Once those were rebuilt - no more problems. Strictly an empirical observation.

Thanks for all the suggestions! I've got some things to look at now.

I like the idea of a portable 02 senser, that would certainly give me some direction. If the snow holds off this week I'll get it out for some testing.


Curt, I do have some very slight play in the shafts, but's I've seen much worse and my idle is pretty good. My understanding is that loose shafts ususally only cause idle issues. Once under load there's so much air going through that the small amount that can leak past the shafts is irrelevent. But I'm no expert on this, just what I've heard.

Anything can be run at an AX, some....like a 930... are just painful to watch.

I do agree with your ignition comment. A multi spark CD system (MSD et al) is a Godsend for carbed motors.

Hello Bill, did you ever reach a verdict on your running woes ?

My engine displays all the symptons that you describe in your first post here and I`m just considering my next move.

Regards, Mike

I believe the issue may be explained as the check valves in the accelerator pump system (three unique ones) are not closing well due to age. These three valves are:

1. The check valve in the bottom of the float bowl is first in the system. Age issues would be corrosion with resulting damage of the brass seat or the stainless steel ball that creates the seal. Check accel pump operation with the top cover off and look for swirling in the fuel chamber which would indicate fuel being pumped past the normally closed valve.
2. The last check valve(s) are the three that hold the accelerator squirters in the throttle body. They may be suffering the same issues as the valve in the float bowl.
3. The last valve is a flapper valve that consists of the rubber gasket and the aluminum disc that are pressed to the inside of the accelerator pump body and close the three little orifices on the back of the pump body. If the gasket is imprinted/old -or- if the aluminum disc is not FLAT -or- if the three little orifices (nipples) are not flat to the pivot points in the bottom of the pump body the flapper valve will then operately ineffeciently.

If any of the above are partially working then the fuel will drain from the squirters leaving you with a late fuel delivery upon throttle application. Rapid pumping of the accelerator pedal will refresh the fuel to the squirters thereby providing the instant response you are missing.

Paul Abbott
Performance Oriented