Lew Shaw Posted January 13, 2018 Share Posted January 13, 2018 In addition to my Corvette, I have a matching Corvette Yellow '34 Plymouth Streetrod called the “Blown Banana”. It has a Chevy 350 with a BDS 471 GMC blower and a 780 Holley single carb with a Holley “Blue” fuel pump. In all the years I have owned it, I have never had it run right. Several “expert tuners” have fiddled with it with no good results and I know nothing about tuning myself. For example, right now I can cruise effortlessly but if I stomp on the loud pedal, it will often hesitate and then backfire through the carb (usually blowing the power valve!) and it will do the same if I romp on it from a standing start. My instinct tells me that at that moment, it has gone dead lean but I don’t know how to correct it. I was wondering if one of my fellow Aceholes could direct me to someone who knows old school tuning and can get this car running as it should run before I'm too damned old to drive! Thanks! Lew Shaw Link to comment Share on other sites More sharing options...
JLs Mistress Posted January 13, 2018 Share Posted January 13, 2018 Lew it can all be traced back to being yellow if it was black need I say more .. Link to comment Share on other sites More sharing options...
az57chevy Posted January 13, 2018 Share Posted January 13, 2018 Ask for Dave at Chuck's Speed Center https://chucksspeedcenter.com/ Link to comment Share on other sites More sharing options...
Extender32 Posted January 13, 2018 Share Posted January 13, 2018 Are you sure it's lean? I'm thinking maybe just the opposite. Link to comment Share on other sites More sharing options...
dale68z Posted January 14, 2018 Share Posted January 14, 2018 hesitation and backfire through carb is a lean condition. I assume it runs awesome if you slowly accelerate to full throttle. I would talk to Bob Ream at imagine fuel injection. He is a carb guru. Link to comment Share on other sites More sharing options...
Dvl4evr Posted January 14, 2018 Share Posted January 14, 2018 Since it has never worked well for you, perhaps you should go EFI Instead. Then you can tune with a laptop. Just a thought from someone who doesn't know poo poo. 1 Link to comment Share on other sites More sharing options...
JohnU Posted January 14, 2018 Share Posted January 14, 2018 Pictures of the Yeller Plymouth??? Link to comment Share on other sites More sharing options...
Bromley's Corvettes Posted January 14, 2018 Share Posted January 14, 2018 Why dont you put a air fuel ratio gauge on it:) Link to comment Share on other sites More sharing options...
Bromley's Corvettes Posted January 14, 2018 Share Posted January 14, 2018 I have a 1050 CFM ProForm carb you can try I bet it will fix your problem:) Link to comment Share on other sites More sharing options...
anmracing2 Posted January 14, 2018 Share Posted January 14, 2018 Maybe you need a higher PV or the shooter might be too small. Check the vacuum of the engine compared to the PV size and also make sure the shooter is squirting on both sides. I would say to also change to a shooter that has a arm to squirt farther into the carb. Ck for vacuum leaks too. 1 Link to comment Share on other sites More sharing options...
anmracing2 Posted January 14, 2018 Share Posted January 14, 2018 Oh yeah, also ck the accelerator pump. If it's old, maybe the diaphram needs to be changed. Maybe even convert to a 50cc pump if it isn't already. I bet Bromley could figure this out for you. 1 1 Link to comment Share on other sites More sharing options...
Lew Shaw Posted January 14, 2018 Author Share Posted January 14, 2018 Thank you all.... JL - John, we all know that YELLOW is MUCH faster than black! az57- will do, if no better option. Thx. Ext32 - Greg, sorry, but lean it is. dale68 - Yes, it does. Sorry, but Bob Ream screwed me back when he worked at Chuck's Speed Center. DVLA - Way too expensive and not the answer. Thx for your response. JohnU - I'll try for some photos. Bromley - I believe I know what is happening, I just don't know how to fix it. Just as dale68 surmised, it runs like a raped ape if I accelerate very slowly. I don't think a bigger carb is the answer since it appears to get all the fuel it need EXCEPT at the hit of the throttle. However, very kind of you to offer the loan of the 1050. Thanks! anm - Heck, if I knew all that I wouldn't have asked for help! BTW, a blown motor is usually only producing vacuum at idle or very light throttle. Just a tap of the pedal and my gauge goes from vacuum to boost. Thanks again to all! Lew Link to comment Share on other sites More sharing options...
Lew Shaw Posted January 14, 2018 Author Share Posted January 14, 2018 JohnU, I hope this works! Link to comment Share on other sites More sharing options...
Bromley's Corvettes Posted January 14, 2018 Share Posted January 14, 2018 I said air fuel gauge not a vacuum gauge. If you see how lean its going on a gauge it will confirm 100% that you need more fuel. Sounds like you need a dbl pumper carb with a much bigger pump shot like anmracing2 said and probably bigger jets in secondary's. If your carb is vac secondary thats your problem. Its not dumping in enough fuel when you go wide open. I also have 850s if the 1050 scares you:) I have tuned small blower engines be four and its pretty crazy how much of a shot of fuel it needs when you first open throttle. I think its because the air speed is so high the velocity is way up there. Like it sucks super hard so fast it needs a bigger shot of fuel or it goes super lean. 1 Link to comment Share on other sites More sharing options...
Lew Shaw Posted January 14, 2018 Author Share Posted January 14, 2018 Bromley, I know you said A/F gauge (I don't have one), but I was actually answering anmracing2. Mine is a double pumper Holley with mechanical secondaries. The 1050 doesn't scare me but I think (according to BDS) that the one I have is adequate and flows the correct amount of air for my motor. But, as you stated, it is not flowing enough fuel at the proper time. You said, "its pretty crazy how much of a shot of fuel it needs when you first open throttle. I think its because the air speed is so high the velocity is way up there. Like it sucks super hard so fast it needs a bigger shot of fuel or it goes super lean" and I think that you are absolutely 100% correct. Now, all I need is someone that really knows how to set up the carb to handle that issue. Unfortunately , that is beyond my level of expertise! Lew 1 Link to comment Share on other sites More sharing options...
anmracing2 Posted January 15, 2018 Share Posted January 15, 2018 LOL! Sorry I guess I should have started by recommending Broms, I was just throwing some ideas as to some stuff to look at when working on a carb. 1 Link to comment Share on other sites More sharing options...
Bromley's Corvettes Posted January 15, 2018 Share Posted January 15, 2018 LOL anmracing if we only knew of a shop that specialized in working on Classic cars and tuning carbs:) I have heard of one over by Curry on 800n miller rd:) 1 Link to comment Share on other sites More sharing options...
anmracing2 Posted January 15, 2018 Share Posted January 15, 2018 Carbs rule, love building them but I never have time. Last carb I've built was for M~'s Imaginary a few years back and it's still kicking ass. Link to comment Share on other sites More sharing options...
Azmotorhead Posted January 16, 2018 Share Posted January 16, 2018 Have you tried dialing back the timing. 90 % of supposed carb issues are actually timing. Check to see what your base timing is then figure out how much mechanical adv is being thrown in. Thoughts to think about: If youre at 14* of initial timing at idle with vacuum adv hooked up pulling in another 16* Youre now at 30* of timing at idle with everything running just fine. Now you stab the throttle and vac drops to 0 essentially dropping 16* of advance the vac adv was pulling in. This is not even taking into account any mechanical adv you may have running Link to comment Share on other sites More sharing options...
Lew Shaw Posted January 17, 2018 Author Share Posted January 17, 2018 Thanks, Azmoterhead. I have no vacuum advance and the timing is set at 38 degrees total, all in at 1800 rpm. Link to comment Share on other sites More sharing options...
Final Effort Posted January 19, 2018 Share Posted January 19, 2018 you say it's a 780 Holley it's been a some time but a 780 = list # 3310. If I'm correct that is a single pump carb. you need to start with a double pump carb that should help things. Look for the List # on the air horn of the carb for an exact carb model. Another question is, how long have you owned this car? Was it ever a wine color? If so I've known this car since the late 60's. Link to comment Share on other sites More sharing options...
Lew Shaw Posted January 20, 2018 Author Share Posted January 20, 2018 Thanks for the reply, Final Effort. My error, I was going from memory (not a good idea at my age!) and the carb is actually a 750 CFM Holley Double Pumper with no choke and mechanical linkage. It's a chore to remove the air cleaner to see the air horn and I really don't care what the number is. Here is a photo. Please go back and read my original post, all I asked was if anyone could recommend a good old school tuner. No, it was never wine color. I bought the car in August of 1982 and it was an all original 1934 Plymouth PFXX R/S Coupe with a lot of surface rust in the OEM Fisherman Blue paint. I spent every Saturday for the next 6 years doing a frame off and modifying it to what it still is today. I have won over 100 top trophies, including my class at the World of Wheels and it has been been featured in 3 magazines. I did all of the planning, engineering, fabrication, assembly and the grunt work. I had to have others do the engine build, paint and upholstery. Even though it never ran like I thought it should, I did manage to put over 45,000 miles on the clock, travelling to many events! Link to comment Share on other sites More sharing options...
Lew Shaw Posted January 23, 2018 Author Share Posted January 23, 2018 Pictures from the past........ Link to comment Share on other sites More sharing options...
JohnU Posted January 23, 2018 Share Posted January 23, 2018 Sweet! That's what we like.....before and after photos!!!! Link to comment Share on other sites More sharing options...
Chameleon Posted January 23, 2018 Share Posted January 23, 2018 Ya ever notice how in these before and after pics, as the car looks newer, the owner looks older? Link to comment Share on other sites More sharing options...
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