[Glenn Lever]

Ok, Dragster Update.
http://forums.maxperformanceinc.com/...ragster+update

Went club racing and it did the same thing again, what is that?

It starts out the evening fairly well, it does not idle great but will stay running.

As the evening progress the idle gets worse to the point that it is hard to keep it running.

On the last run before I gave up for the evening, I was sitting on the line with the trans brake on and it tried to die out on me.

Here are some facts, compression has been checked, valve lash has been checked, timing has been checked, cap and rotor checked and will be replaced, new plugs installed and gapped at .350 (MSD box 6AL-2), Carb has been pulled apart cleaned and reassembled (QuickFuel QFX 4710-A 1050CFM Alcohol) .

I got 11 straight runs at Indy in with no problems (over three days, the mid day was a rain out).

These evening races total 7 passes and I cannot make all seven of them.
Runs are very consistent at 8.90, under load and at RPM it runs great, at idle or when shifting it runs bad.

The engine is the engine that came out of the Firebird and ran a whole season with gas with no problems.

We switched to alcohol because of the overheating problems (never above 220) and now it will not idel.

New air bleeds are on order.

It is the front half of the engine that is not running right in that the EGTs on those cylinders are low. The front two cylinders are not firing at all when idling at the end of the evening.

The thinking is the front half is either way to rich or way to lean.

Ideas??????????????????????????

[Tom Vaught]

Look at the Idle Bypass jet (would be my first guess but I am not a mechanical FI expert). Sounds like excess fuel is flooding the cylinders at low speeds.

Tom Vaught

[Glenn Lever]

Originally Posted by Tom Vaught

Look at the Idle Bypass jet (would be my first guess but I am not a mechanical FI expert). Sounds like excess fuel is flooding the cylinders at low speeds.

Tom Vaught

This is not mechanical FI, has the largest Mallory electric fuel pump with matching fuel bypass regulator. Data recorder records fuel pressure, there is a spike to 10 pounds but never drops below 7

[twooldgoats]

Originally Posted by Tom Vaught

......I am not a mechanical FI expert.....
Tom Vaught

He's running a carb.

Jim

[johnta1]

It is too rich.

Needles are probably not seating.

Make sure the float and needle assembly is made for alcohol.

Also, the bypass regulator may need some work.
If it's not bypassing enough fuel, it could be causing the carb to flood over.

[Probird]

If you look down the carb are the boosters dripping fuel? I agree with John, sounds like the fuel is getting by the needle and seat and flooding it. Have you played with the idle adjustment screws? What happens when they are turned all the way in?

[Glenn Lever]

Originally Posted by johnta1

It is too rich.

Needles are probably not seating.

Make sure the float and needle assembly is made for alcohol.

Also, the bypass regulator may need some work.
If it's not bypassing enough fuel, it could be causing the carb to flood over.

Carb has site windows in the bowl, fuel is half way up the window and stays steady.

Carb is a Quick Fuel carb made for alky
http://www.quickfueltechnology.com/c...m-alcohol.html

Fuel pressure is logged on the data loged on the data loger. It does spick to 10 PSI just after lunch but does not drop below 7. Fuel pump and regulator are matched

[Glenn Lever]

Originally Posted by Probird

If you look down the carb are the boosters dripping fuel? I agree with John, sounds like the fuel is getting by the needle and seat and flooding it. Have you played with the idle adjustment screws? What happens when they are turned all the way in?

Have used a uni-syn to balance fuel idle screws, if screwed all the way in engine dies.

Engine actuall idles better with Uni-Syn choking a barrel. Also when flushing the system of alky with gas engine idles pretty nice.

Choking one barrel and idleing on gas, needs more alky when idleing????

[screamingchief]

I was looking over your post at that "other" forum,did'nt really have a good answer for you,but I had noticed a few things that I did'nt care for in the way ya'll set-up that fuel system.

The most important thing about the fuel system set-up is you should'nt really run that bypass leg from the regulator back to the filter like ya'll did,it really should've been run back to the cell itself instead,as that eliminates the chances of aerating the fuel,also it wont affect the pump output when a whole bunch of fuel is being bypassed during times of low demand.

And BTW the Comp 140 is'nt the biggest Mallory pump,the Comp 250 pump is,and IMO the Comp 250 would be a much better pump for a dedicated alcohol set-up,especially when a few other changes to the fuel system set-up would be made to accomodate that pump.

And with that Comp 140 pump,you gotta remember to disable the pumps internal bypass when using it with a return regulator,so that maybe another area to look into as well.

But I really dont think any of that ^^^^ has anything to do with your current problems.

One thing that did come to mind is you said you had the QF carb apart,cleaned and re-assembled and such,mind if I ask,were new gaskets used when doing so?

I ask because with domi's,you gotta be sure to not mix up the 2 circuit MB (metering block) gaskets with the 3 circuit MB gaskets.

Also,drain all the fluid from those small liquid filled fuel pressure gauges!

I say that because that glycerine in those liquid filled gauges will adversely affect the readings they give,so often what happens is the pressure in the system is'nt really what's showing on the gauge,and as a result guys often set the fuel pressure based on incorrect readings.

I also agree that it would be a good idea to give the floats and the N&S a good once over again too.

That,and as always be sure to check closely for any vacuum leaks.

Just some food for thought,hope it helps.

Bret P.

[Jack Gifford]

With a couple of cyllinders rich enough to keep them from firing, I'd expect to see/feel/smell plenty of liquid alky out of those two header pipes.

[Glenn Lever]

Originally Posted by pontiac jack

With a couple of cyllinders rich enough to keep them from firing, I'd expect to see/feel/smell plenty of liquid alky out of those two header pipes.

No fuel dripping from the header pipes. This did happen when we first test a barrowed carb to see if it would correct the over heat problem when it was running on gas. the alky dripped out the center four cylinders.

[Glenn Lever]

Originally Posted by screamingchief

I was looking over your post at that "other" forum,did'nt really have a good answer for you,but I had noticed a few things that I did'nt care for in the way ya'll set-up that fuel system.

The most important thing about the fuel system set-up is you should'nt really run that bypass leg from the regulator back to the filter like ya'll did,it really should've been run back to the cell itself instead,as that eliminates the chances of aerating the fuel,also it wont affect the pump output when a whole bunch of fuel is being bypassed during times of low demand.

And BTW the Comp 140 is'nt the biggest Mallory pump,the Comp 250 pump is,and IMO the Comp 250 would be a much better pump for a dedicated alcohol set-up,especially when a few other changes to the fuel system set-up would be made to accomodate that pump.

And with that Comp 140 pump,you gotta remember to disable the pumps internal bypass when using it with a return regulator,so that maybe another area to look into as well.

But I really dont think any of that ^^^^ has anything to do with your current problems.

One thing that did come to mind is you said you had the QF carb apart,cleaned and re-assembled and such,mind if I ask,were new gaskets used when doing so?

I ask because with domi's,you gotta be sure to not mix up the 2 circuit MB (metering block) gaskets with the 3 circuit MB gaskets.

Also,drain all the fluid from those small liquid filled fuel pressure gauges!

I say that because that glycerine in those liquid filled gauges will adversely affect the readings they give,so often what happens is the pressure in the system is'nt really what's showing on the gauge,and as a result guys often set the fuel pressure based on incorrect readings.

I also agree that it would be a good idea to give the floats and the N&S a good once over again too.

That,and as always be sure to check closely for any vacuum leaks.

Just some food for thought,hope it helps.

Bret P.

A lot of good thoughts.

You are not the first to comment on the routing of the bypass leg. The tank only has one bung in it. I am thinking on pulling the tank cleaning it and welding in a second one.

I have searched Summit for the Comp 250 but cannot find it. Does not mean it isn't there. The 140 is the largest one I find that is rated for Alcohal. I do not think fuel delivery and pressure is the problem, aeration of the fuel at low RPMs could be the answer and a bigger pump would only make that problem worse. The bypass to the tank would solve that problem if it is the problem (I like the idea, it makes sense and fits the smpontons).

I have a data logger and fuel pressure is captured at the carb. fuel pressure peaks at 10 PSI just after the lunch, and never drops below 7.

New gaskets were used, I rebuilt it once, and a professional tuner rebuilt it once. I am a novice, could have reassembled incorrectly, however being a novice I was very careful, looked at everthing as it came apare, compared holes and the impression in the old gaskets to make sure it went back together the way it came apart. 2 circuit metering block gaskets were used. Also the reason the carb was taken apart the first time is because of the problem, and it got 11 runs in Indy where there was no problem. (crab had to be right for those runs).

Glycerine in gauges, incorrect readings. Interesting. I have two fuel pressure gauges and the data recorder sensor and they all say the same thing.

We will try the new smaller air bleeds, I do not think this will solve the problem. Monday Matt will have an alky engine on the dyno. We will try this carb on that engine and that carb on this engine. this should elimate the carb.

I really like the aeration suggestion and will pursure that.

Your reply was of great help and much apprecaited!

[beastmaster]

I had a thread asking questions of Quick Fuel Alky carb 950 worked those issues out . We were still working on the car since then and had'nt ran it at the track yet. This week started doing the same thing yours is . My friend just called me a minute ago and found at the hit of the throttle it's pulling the bowls dry, fuel pressure is good but with adjusting the floats almost below the sight suppose to run great they rev motor up to 6 grand an didn't miss. Won't no anymore until i get track time. Good Luck! Suppose to be and issue with Alky carbs, his is brand new also

http://forums.maxperformanceinc.com/...d.php?t=666453

[Glenn Lever]

The bypass has been disabled per the directions included with the pump.

The QFX Alky carnb is a two circuit while all the rest are three (confirmed with Quick Fuel)

We will be going to the track tomorrow and are chaning the following things.
bypass will go into the tank, not a tee before the fuel filter.
new cap and rotor
smaller air bleeds on the low speed circurt in the carb

[screamingchief]

The Comp 250 pump for use with alcohol is the #5250A part number.

Here is a link @ Summit:
http://www.summitracing.com/parts/MAA-5250A/

The good thing about this pump is it has an external bypass instead of the internal bypass like the Comp 140 pump has,and the Comp 250 pump is much more "flexible" pump in terms of how it can be plumbed.

BTW,did you guys disable the Comp 140 pumps internal bypass?
If not you really should do that when using that pump with the bypass reg.
(see note from the Mallory reg instructions vvvv below)

With the external bypass on the Comp 250 pump,most high demand applications will use the bypass from the pump instead of using a bypass regualtor,and they'll then use a dead head reg like the "big" holley reg #12-704 item,and then they often add a small fixed orifice bleed/bypass @ the reg. to control any "pressure creep" issues or such.

As Beastmaster alluded to,pressure only tells part of the story,volume is often the untold story that causes a lot of people headaches,but again your problem seems a bit different as yours is happening during low demand/peak bypass conditions.

Anyhow,,,enough about pumps & fuel system design...

As for the carb,from the info in the quick fuel catalog,it clearly states that all the gas QFX domi's are 3 circuit carbs,though I have no idea what the ALKY carbs use,so that is kinda still a ??? for me at this point.

MB text from QF catalog included vvvv below.

Might be a good idea to contact the tech line at quick fuel confirm what MB gaskets the ALKY QFX carbs use.

Sorry about the post jumping around on you Glenn,had to edit this post and it was easier to just delete,correct & re-post this post.

HTH

Bret P.

[Pontirag]

and remember that alcohol is very corrosive so you might want to go through the entire system and evaluate it for compatability. the rubber stuff too

[Glenn Lever]

Originally Posted by screamingchief

The Comp 250 pump for use with alcohol is the #5250A part number.

Here is a link @ Summit:
http://www.summitracing.com/parts/MAA-5250A/

The good thing about this pump is it has an external bypass instead of the internal bypass like the Comp 140 pump has,and the Comp 250 pump is much more "flexible" pump in terms of how it can be plumbed.

BTW,did you guys disable the Comp 140 pumps internal bypass?
If not you really should do that when using that pump with the bypass reg.
(see note from the Mallory reg instructions vvvv below)

With the external bypass on the Comp 250 pump,most high demand applications will use the bypass from the pump instead of using a bypass regualtor,and they'll then use a dead head reg like the "big" holley reg #12-704 item,and then they often add a small fixed orifice bleed/bypass @ the reg. to control any "pressure creep" issues or such.

As Beastmaster alluded to,pressure only tells part of the story,volume is often the untold story that causes a lot of people headaches,but again your problem seems a bit different as yours is happening during low demand/peak bypass conditions.

Anyhow,,,enough about pumps & fuel system design...

As for the carb,from the info in the quick fuel catalog,it clearly states that all the gas QFX domi's are 3 circuit carbs,though I have no idea what the ALKY carbs use,so that is kinda still a ??? for me at this point.

MB text from QF catalog included vvvv below.

Might be a good idea to contact the tech line at quick fuel confirm what MB gaskets the ALKY QFX carbs use.

Sorry about the post jumping around on you Glenn,had to edit this post and it was easier to just delete,correct & re-post this post.

HTH

Bret P.

I used the link and in the notes at the bottom "These Comp Pump series electric fuel pumps are ideal for high performance street or race applications. They have a high-quality, permanent-magnet 12 V electric motor and feature factory-set base pressure. Intended for gasoline use, each pump assembly features a quiet, high-efficiency Gerotor design that provides stable output. The housings are fully machined and have a special design that allows for some adjustment of the output pressure. All Comp Pump series fuel pumps must be used with a fuel pressure regulator. The pumps are available in many different ratings, from 60 to 500 gph, with fuel pressure ranging from 4 to 100 psi. They're perfect for any carbureted or fuel injected engine!"

[Glenn Lever]

Originally Posted by Pontirag

and remember that alcohol is very corrosive so you might want to go through the entire system and evaluate it for compatability. the rubber stuff too

I have no rubber hose anywhere in the system. The hard lines however are not coated and I flush the system after each weekend.

[johnta1]

The 'A' on the end is for alcohol.
I used the Comp 250 pump when I ran alky carbs.
The pump has a different diaphragm for the alcohol.

The pump worked great.
(the carbs were a pain, ran great when good, but screwed up easily)

You also need the alcohol regulator to go with it.
The diaphragm is made for alky also.

[Glenn Lever]

Originally Posted by johnta1

The 'A' on the end is for alcohol.
I used the Comp 250 pump when I ran alky carbs.
The pump has a different diaphragm for the alcohol.

The pump worked great.
(the carbs were a pain, ran great when good, but screwed up easily)

You also need the alcohol regulator to go with it.
The diaphragm is made for alky also.

Ok, the notes must just be generic.