SU carbs spitting fuel, cause? [race car]

[Stick]

I bought a bugeye racecar last fall, and have been trying to get it tuned up and running right. The car seems to always run rich, and in the process of trying to tune it up I noticed that the carbs are spitting fuel. I think this might be part of my problem, but I don't know what is causing it? This is my first time working on SU carbs (or any carbs in any detail) so I am lacking lots of experience with them.

Some things to know, this is a 1959 948 racecar with modified carbs and modified N/A engine built to run and running on 110 leaded fuel. I don't know the full extent of the modifications but at the very least it is running an aggressive cam, and possibly a lot more done to it. Where normal carbs have a flat spot at the bottom by the jet, mine are rounded out. Also, fuel PSI is usually around 6-7 PSI. This is about twice as much as normal I am told. However, when I remove the top of the float bowels I am able to stop the flow by lifting the float with my finger so I don't <span style="font-style: italic">think</span> it is a simple case of flooding the carbs from the PSI. Also, when I turn the fuel pump off the carb still spits right up until it runs out of fuel.

Does anyone know what could be causing this or things I should be checking? Also, I can take and post pictures of anything that would help you help me figure out what is going on here.

Edit: Also, compression is good (180-200 cold on all cyls)

Thanks

 

[JPSmit]

Re: SU carbs spitting fuel, cause?

Any number of causes.

Other racers may jump in but, 6-7 psi is more than twice - on a regular car it is more like 2-3 psi.

I had a similar problem and it turned out to be timing

 

[Bob Claffie]

Re: SU carbs spitting fuel, cause?

Check the dashpots for light oil. Some racers leave them empty. Bob

 

[Bayless]

Re: SU carbs spitting fuel, cause?

When you say the bottoms of the carbs are rounded instead of flat, I'm assuming you mean the venturies (chokes in Brit speak). I have heard of some serius racers doing that but it really changes the characteristics. The first thing that comes to mind though is that lowers the jet and puts it below the float level unless something else has been done to correct for it. That will surely make it flood. Also, the pump pressure is way too high which yields the same result.

The main problem in reducing the venturi restriction is it reduces the vacuum that pulls fuel through the jet. Maybe its possible that the PO went to a higher pressure pump to soft of force some fuel in, help in gthe vacuum a bit. Maybe that works when running flat out all the time but it sure seems like a dangerous way to do it. Well, some of our racers will come along soon and probably have some better ideas for you.

 

[Stick]

Re: SU carbs spitting fuel, cause?

Well, as it turns out my dashpots are dry. I tried to find some 20 weight oil locally last fall to put in them and couldn't find any. I ended up using some 5W30 I had around just to see, but I just checked and that has diapered now. I've heard of people using ATF, should I get some of that and see if that helps?


Here are some pictures of the carbs. Probably easier than trying to describe the modifications.

One of my modified carbs, note the bottom is rounded smooth

Here is what I believe is a stock one (from one of my bins of parts that came with the car). Note the raised section on the bottom is present on the stock carb, but not on mine as seen in the background.

Here is a couple pictures of the overall setup. I'm not as familiar with the stock setup as most of you as I've never had a stock one, but I think there are quite a few differences here.

Does that help? I can provide more pictures if needed.

 

[Roger]

Re: SU carbs spitting fuel, cause?

Under what conditions is it spitting back? If it's only at idle, You may not have cause to worry. Camshafts with a lot of overlap, and ealry inlet-valve opening, quite often do that. Try increasing your idle speed and see if it gets better.
I helped build an A-type mini 998 engine for a friend with the BMC 649 camshaft and it would never idle below 1300 rpm or so.

 

[jvandyke]

Re: SU carbs spitting fuel, cause?

I get it, the "threshold" area around the jet is gone. Like Bayless said. That's a pretty drastic mod isn't it? Why does that material run across the entire bottom of the carb in the first place? Seems it's there to increase air velocity and draw in fuel? Removing it "let more air in"? Interesting. Skeptical.

 

[texas_bugeye]

Re: SU carbs spitting fuel, cause?

SFD is still in Dallas contact them mybe thet can give you some info on the cam and the carb setup?
SFD Engines
214) 553-0051
10755 Mapleridge Dr
Dallas, TX

 

[Stick]

Re: SU carbs spitting fuel, cause?

OK, I've got a lot more info now so prepare for a long post.

Roger: Increasing the idle speed fixed the spitting problem, I re-balanced and re-adjusted the mixture at the faster idle and it runs well now.

jvandyke: You are correct, it is a rather drastic mod. Turns out the motor wasn't designed to be run below 5k RPM. More on that later.

texas bugeye: My car is also a '59 948 AN5Lxxx VIN from Dallas as it turns out. It lived in the Dallas area as a yellow bugeye race car up until the late 70's.

I called the number you posted, SFD is not really in business anymore. The guy is Bob Webber and he is retired and only projects on the side, and very little to do with sprites anymore. HOWEVER, he was a gold mine of information on the car... As it turns out, he owned this very car at one time and it lived in his shop under several owners for over a decade. He remembered the car in great detail and even gave me an ownership history dating back to 1968, where his info stopped is exactly where mine picked up in terms of who owned it so I now have a complete picture. Pretty neat considering this car hasn't been sold with a title for 40 years since its been a race car, there is no paper trail to speak of. I'm going to get with the texas SCCA and see if I can dig up some of its race history now that I have names to put with the car. He told me about some of the unique modifications that had been done to the car including custom leaf springs to allow for wider tires, tortion (I think it was?) bars in the back, and then the motors (yes i have more than one) and carbs that he built himself. Even told me about one race where another car spun out and caught mine on the right rear corner and he ended up cutting out part of another bugeye and welding it in. Sure enough, I crawled back into the back of the car and there were welds right where he said they'd be. The job was very well done, looking at the outside you can't tell at all and I never even knew it replaced until he told me to go look at it. I've been working on this car for the last 9 months off and on getting it running again and feel I know the car pretty well. This guy knows it way better inside and out, and he hasn't seen it in 30 years... Talk about amazing.

Now for the bad news... In the hour and a half I talked to Bob tonight, it became clear that these engines are not for me. The larger problem I've been having here in the last week is the car smoking very badly when running. I had hoped it related to a carb problem, hence this thread on the spitting fuel issue because I thought it could be related. Turns out that's normal (with this engine build), and goes away at higher RPMs and can be fixed with a higher idle like Roger said above. After talking to Bob we determined that the smoke is probably due to a failed piston ring seal. I have plenty of spares and can fix that right up so that isn't a big issue. But the problem is, these motors are built as full on race motors and don't even start to make power until 6,000RPM. You are not supposed to give it full throttle until you are above 5,000RPM or the engine will detonate and eventually damage the piston rings. Since I didn't know, I had been feeding it the beans from about 3,000 RPM and created a problem without knowing it. But, the bigger issue is that I have neither the skill nor the time to maintain these custom engines. They are designed to be rebuilt after every few races (12-15 hrs running time is probably pushing it) simply due to the extreme nature of the modifications to the carbs and engine it is not conducive to street use. I intend to race, but I want to be able to cruise around the countryside too and the simple fact of the matter is I won't be able to do it with these motors. They need to be used in a dedicated vintage race car and that is a hobby I can't afford to take on right now.

I am finding myself both very excited and very sad at the same time. On one hand I learned a lot about the car and its colorful history. But on the other hand I also learned that I won't be able to use the two engines I was very proud to have and will have to let them go. Given the history of the car and the custom work done on both the car and the engines it only seems right that they stay together. But I have grown very attached to the car and really want to keep it and swap in a more workable powerplant (1275 maybe?). I already have bought parts and made detailed plans for what I want to do over the next several years with the car so I have a tough decision ahead of me... Do I sell the engines, car, and assorted spare parts (tons of them, literally) as one to keep the history in tact? Or do I be a bit selfish and keep the car for myself, sell the engines, and ebay the boxes of parts piece by piece?

 

[Stick]

Re: SU carbs spitting fuel, cause?

Here are some pictures of the fun I've already had in the short time I've had this car.

Cruising on the highway (picture taken from my friend's bugeye)

A cool bugeye to bugeye shot

Some other Ames, IA spridgets we cruised with that day

Another angle:

Loaded and ready to meet up with the Iowa British Car Club at Greenwood Roadway (a old road course that has not been used since the 70's, it is now deteriorating pretty badly but you can still take a slow cruise around it)

 

[JPSmit]

Re: SU carbs spitting fuel, cause?

I vote for keep the car sell the engines - it's your car, your choice, but, to add to that, while you do have the history,

1. It's the history of the car not the engines
2. While the history is unbelievably cool, the car/ engine combo is neither so rare nor so significant that they are worth keeping together.

So, sell them, build a new one with manageable zip and drive it like you stole it!

 

[texas_bugeye]

Re: SU carbs spitting fuel, cause?

I would sell it or trade it. Your not going to have much fun with a high strung Scalded cat like that as a street machine. But I would have to admit I would want it. I have a few roads near by that I would love to thrash a ludicrous amout of HP from a bugeye at. Very Nice car

 

[Stick]

Re: SU carbs spitting fuel, cause?

Thanks for the input guys. I put in a request to the SCCA for information on the car, although I'm sure it will take some time to track down info 30 years after the fact.

I think I will sell the engines and parts. Any idea what a couple race engines like this could be worth? Both are in great shape. Looking around the spridget and race boards here I have not seen a lot of for sale adds... What would be the best way to go about posting one? Many boards I have been on frown upon posting for sale adds in the general forums and the classifieds don't seem to be all that active here from what I could see.

I'd be looking at unloading a lot of parts (click here to see about half of them) Among other things I have roughly 15 camshafts of various cuts, a box of carburetors and parts, brakes, flywheels (some aluminum), clutches, shocks, diffs, 3 transmissions (2 standard 1 straight cut, only one is assembled). Last winter I got through about half the boxes of stuff, the engine blocks, heads, and engine internals I have not even gotten to yet to take pictures although outside of the two race motors some of them have been largely neglected.

 

[Woblynne]

Re: SU carbs spitting fuel, cause?

That is one sweet bugeye!!

I would sell the engine and enough of the spares so you can get a streetable engine of your spec.

Loving that paintjob!
Mark

 

[bthompson]

Re: SU carbs spitting fuel, cause?

I wouldn't be too concerned about keeping the engines and parts. Race cars eat engines, and unless one of your lumps is the original, they are probably just two in a long string of 'em. Shame in all that extra stuff, there aren't parts that'll just let you de-tune one of the engines and use that. Happy ebaying--looks like you have a gold mine of stuff there.

 

[Bayless]

Re: SU carbs spitting fuel, cause?

Hey, it's really great and exciting to get that kind of history on your car, especially one that really has a history. Also, I agree with most of the above. Race cars eat engines regularly. Those you have are most likely one some of many over the years. The history goes with the car. I thin you would be right to sell those race engines and use part of the proceeds to build a proper streetable one.

 

[Bob Claffie]

Re: SU carbs spitting fuel, cause?

It should be possible to detune either or both of those engines. Simple fix would be a closer to stock cam. Next check to compression to make sure it's not extremely high. Thirdly check piston to wall clearances. Maybe have to replace the valve springs. On second thought sell 'em. Bob

 

[Stick]

Re: SU carbs spitting fuel, cause?

It should be possible to detune either or both of those engines. Simple fix would be a closer to stock cam. Next check to compression to make sure it's not extremely high. Thirdly check piston to wall clearances. Maybe have to replace the valve springs. On second thought sell 'em. Bob

Yeah, I asked the guy who built them about that when I had him on the phone. Changing to a milder cam would send compression through the roof, leading to a whole bunch of other stuff needing changed. It IS possible, but it is not really a good option. Besides, these engines do what they are supposed to do so well they really just need to be in a good home where they can do their thing.

 

[Hairyone]

Re: SU carbs spitting fuel, cause?

Sell um to a racer IS the only option. De-tuneing will not be posible without a compleet re-build & a hole lot of new parts. One trick on a race engine is to use main & bigend bearings that are slightly oversized. This reduces internal friction in the engine, and achieve a few more horses. It will also wear out quickly, hence the 12hours between re-build.

What a beautiful car.
You'll need a slightly hot engine in this. Good luck

 

[Hap Waldrop]

Re: SU carbs spitting fuel, cause?

I'll admit, I did take the time to read all this. Those are SFD, AKA Bob Weber of Texas thru bore race carbs, Bob is a smart guy, built fast racing stuff. On a thru bore SU carb, the bridge is machined out of the carb throat to increase the CFM of the carb, but it pretty much makes it un streetable, so life with those carbs, which were menat for race only condition is going to be tough to live with oin the street. Next, I guessing this is still a 948 HP, car, most of the time those engine has ungodly compression ratios, real high lift cams, so not streetalbe either. SO if you trying to street drive this car with a full prep 948 it aint's gonna work, these engine needs the ehad gasket changed every 100 miles or so, totla refresh/rebuild every 30 or so miles. I raced these cars for 25 years, if you know what you have and want to talk about it, call me.