Lazeum Posted January 24, 2009 Share Posted January 24, 2009 Good to hear about you and your trials Weather is not so nice currently in France so the Z is hibernating for some weeks (not months as it was in Michigan!!) I have 165 air jet I can try but first thing will be timing. Since we have the same "problem" with completely different engine (cams, volume, head, etc.) I assume somethingis going on. I'm wondering if the fuel supply cannot be a reason as well. I have a mech fuel pump and a pressure regulator. I'm wondering if the overly rich condition cannot be from bad management of fuel pressure from the pump & regulator. I'll give a try with my other pump (elec) and see how it goes. So far, I just check weather forecast everyday I wish weather was better! Quote Link to comment Share on other sites More sharing options...
zredbaron Posted January 24, 2009 Share Posted January 24, 2009 i have an electric fuel pump mounted near the tank. i dont remember the brand, but it is a centrifugal pump that is high-flow, low pressure and cost a pretty penny. if my memory serves, the pressure is in the 3.5 psi neighborhood. of course it *could* be fuel pressure. it could be mixture. it could be timing. it could be cam/block. it could be venturis. it could be floats. it could be anything. we're stabbing in the dark here. we're trying one thing, finding no change, then sprinting to the next idea that produces the "well, maybe..." sentiment. at this point im tired of chasing "hey it might be this..." we may have similar problems in that we both have unexplained dips in the AFR, but yours is minor, and mine is severe. the problem may be in fact be from some problem we have in common, and it may be from a limitation of carbs vs. fuel injection. lets not forget that there are very good reasons that all cars are fuel injected these days. lets face it, there are some very complicated fluid dynamics going on in these wonderful carbs (and they are quite wonderful), and everything we know about them is 'theory.' the designs are no doubt based on many years of experimentation. they can't possibly feed any given engine demand that can be built, can they? i have been chasing this with my wallet for years. i have had hope, promise and eagerness in trying new parts or adjustments, and nothing has helped. the one thing that has been constant is that the more i've upgraded the engine, the worse the dead spot has become. when the block and head were stock L24, the driveablity (and therefore AFR curve) was perfect. after my first round of upgrades, it was still pretty decent. after the next, there was a tricky spot. after the next it was a problem. and now, at race engine, its an abysmal little black hole in the power band that you really have to be patient and know how to finesse your way through. at this point i am inclined to think that we are experiencing a limitation. you have only a minor dip because you have a street performance engine, and my race engine has aggressively exacerbated this condition and created a nearly undriveable rpm window. but hey, my theory can never be proven, only disproven. so unless/until someone can actually fix my dip, we will never know.... i'm simply saying that i have all the parts and and adjustments and tools that i've ever heard of yet i still have no results. dyno, timing (w/vacuum advance), fuel pressure, jetting, flow balance, floats, cold air, etc etc etc. nothing. they all have had an effect of course, but nothing has even masked the problem. these things have simply made the rest of the band run better or not. the answer i hear is FI. that's not to say i'll do it, but that's the only true solution i see.... Quote Link to comment Share on other sites More sharing options...
Lazeum Posted January 25, 2009 Share Posted January 25, 2009 I understand your frustration. I'm still new to the game, I guess I'm still going to look for improvement. I've logged a "raced" prep engine and 2x 45DCOE (Alpine A110 1600s) around Xmas, the AFR was flat all over the power band. I have hope thou I can achieve the same results! Anyway, rich spot or not, it does not avoid me to move forward. I may have to leave with it, I'm fine with that; without the wideband, it is hardly noticeable ) Quote Link to comment Share on other sites More sharing options...
zredbaron Posted January 25, 2009 Share Posted January 25, 2009 i haven't given up the hope that its possible, i've just lost motivation to keep trying. perhaps i'll come back to it, perhaps i won't. who knows. regardless, best of luck to you, and i trust that you'll share your discovery if you ever do figure it out. cheers. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted January 25, 2009 Share Posted January 25, 2009 regardless, best of luck to you, and i trust that you'll share your discovery if you ever do figure it out.cheers. You can be sure about that Quote Link to comment Share on other sites More sharing options...
didier Posted January 27, 2009 Share Posted January 27, 2009 I understand your frustration. I'm still new to the game, I guess I'm still going to look for improvement.I've logged a "raced" prep engine and 2x 45DCOE (Alpine A110 1600s) around Xmas, the AFR was flat all over the power band. I have hope thou I can achieve the same results! Anyway, rich spot or not, it does not avoid me to move forward. I may have to leave with it, I'm fine with that; without the wideband, it is hardly noticeable ) Don't give up, Mathieu, you are on the right way ! Quote Link to comment Share on other sites More sharing options...
akumazeto Posted February 1, 2009 Share Posted February 1, 2009 Got a question for everyone. My weber pump jet in the rear(tripple weber carbs) its all the way down when I opened the cover. The other two are workign fine but the third one is pushed all the way down on its own. Would this be a problem my my car wont start??? Quote Link to comment Share on other sites More sharing options...
wondersparrow Posted February 2, 2009 Share Posted February 2, 2009 Is the throttle stuck? I dont think that the pump itself being stuck would affect anything other than the fact that it wouldnt do its job, I could be wrong. Quote Link to comment Share on other sites More sharing options...
akumazeto Posted February 2, 2009 Share Posted February 2, 2009 HMmmmm well the throttle seems like its working on the linkage Quote Link to comment Share on other sites More sharing options...
wondersparrow Posted February 2, 2009 Share Posted February 2, 2009 Does it move easily? maybe the spring is broken. If not, Maybe its time for a good cleaning Quote Link to comment Share on other sites More sharing options...
akumazeto Posted February 4, 2009 Share Posted February 4, 2009 Ok so here is the delema. I took out the pump spring the one that goes down and I switched it from the middle spring. The one I switched out still goes down. and the other sits right. What should I do in this matter? Is it repairable adn is it easy to do? Thanks everyone Quote Link to comment Share on other sites More sharing options...
wondersparrow Posted February 4, 2009 Share Posted February 4, 2009 Cant help you there, I dont have a lot of experince with carbs at all. I dont know how comfortable you are taking things apart, but if it was me, I would take apart one that works and one that doesnt and find out what the difference is. On a side note, I have a question for those that do have more experience with these. I am in the process of rebuilding all three of my carbs. It going quite well and I now know a lot more about how they work. I am runnning into one problem though. On all three carbs, the pump jets seem to be really seized in. I have tried carb cleaner, gas, varsol, and a swarm of other hazardous chemicals to try to get them out. I have tried pulling carefully with needle nose pliers, and I have tried pushing them from the bottom using the flat edge of a wrench. All 6 are still stuck in there and I cant figure out how to get them out. I would really like to avoid damaging them. They all seem to work, but as the rest of the carbs are all rebuilt with new parts/gaskets/etc, I would like to clean them up. Any Ideas? Quote Link to comment Share on other sites More sharing options...
Lazeum Posted February 17, 2009 Share Posted February 17, 2009 Just small off topic pictures of Webers to help us going thru this long winter That would be something sweet to do on a Z. Chevy 327 with 4x45DCOE. First challenge would be to find the intake manifold... Second one would be to tune it up! Anybody knows why they drill holes on the top cover cap? I've seen many cars with DCOE with drilled caps lately (all with 45DCOE). The car is a 68 Bizzarrini 5300 GT seen at Paris Classic car show (Retromobile) this weekend This is how the car looks like Quote Link to comment Share on other sites More sharing options...
eds240z Posted March 4, 2009 Share Posted March 4, 2009 i followed you guys through this whole thread and found a lot of good info. still confused!!! my car always stumbled on take off and hard acceleration. but as soon as the rpm's picked up it was cool. then i upgraded my cam to the stage 3 msa and now it hesitates on full throttle. i followed some tips on this thread and did some adjustments. i adjusted the throttle so that it covers the first hole. adjusted the mixture screw and synched the carbs. did not change any jettings. now the car runs strong!!! just feel a little hesitation when i punch it. the onle thing that bothers me now is my eyes are burning from the exhaust fumes. didn't smell this rich before and the car ran like crap!!! it has 40f9 & f11 emul. haven't check the other jets yet. anyone have any suggestions??? what else should i do or change? Quote Link to comment Share on other sites More sharing options...
akumazeto Posted March 4, 2009 Share Posted March 4, 2009 On my set up I was hesitating when I used 180 air f11 tubes and 130 main but when I switched back to 160 air it got better. 40f9. You should try 50f9. When I did that it got better but I guess its all on the elevation where you live. Here in Las Vegas its kinda hard but I make due. If your smelling fumes yeah your running rich whats your PSI on your fuel pump? I was running rich at 4psi and when I went back to 3PSI i dont smell it anymore Quote Link to comment Share on other sites More sharing options...
Lazeum Posted March 4, 2009 Share Posted March 4, 2009 eds240z, you need to give more info on your setup (engine specs, jettings, type of DCOE, venturis?) if you've changed cam, timing could be adjusted a bit as well. I would assume bigger cam brings more air flow at high rpm. Without jet change you might be lean. This is just a guess. I'm also confused with your statement, you say it run strong after some adjustments but afterwards you states it smells gas and runs like crap... Regarding issues, you need to separate them and work one by one: - hesitation to take off with moderate acceleration => transistion circuit - Hesitation when you floor it fast => Acc pump circuit - Hesitation at WOT => Main circuit (main & air jets) As a first comment, I agree with akumazeto: 40f9 for idle jet seems to be a little bit small, I run 50f9 and I'm considering 55f9 with my setup. If you are willing to invest some money ($300-$500 for new setup), your best friend would be a O2 wideband sensor with datalogging capabilities. Quote Link to comment Share on other sites More sharing options...
akumazeto Posted March 4, 2009 Share Posted March 4, 2009 You know thats right. since he has a cam it is better for him to get a 55f9 right? Im using a stock came so 50f9 is good for me. O2 wideband sensor with datalogging capabilities. Yeah thats some serious money but its hella worth it. Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted March 4, 2009 Share Posted March 4, 2009 My friend took his 77 200SX GT3 car to the dyno today. At base and up to about 3500RPM, the car is so rich it won't register on the dyno's O2 sensor. Right when it hits 4000rpm's it spikes super lean - 16:1, then at about 5500-6500, it starts working it's way slowly back down to about 13:1. Weber 50's, (not sure of choke size) 220 main jet and 200 air jet. They swapped in these larger jets from the smaller 200 main 180 airs, and while the problem got a "little" better, there is still this phenomena of the lean spike starting at 4000rpm. Checked float levels. All OK. The car has a radical cam, and due to the way it was built, the cam was advanced 6 degrees. Trying to get a hold of the graph depicting the spike - he's still got it and I will have to get a hold of it and post. Seems awful strange that it spikes lean when the main jets are full on under WOT. Carbs were freshly rebuilt. One would think that if there's cloggage, it would get worse as it gets higher in the rpm range, but strangely enough - it corrects itself. ANY ideas? Quote Link to comment Share on other sites More sharing options...
eds240z Posted March 4, 2009 Share Posted March 4, 2009 sorry guys for lack of info. i'm going to be working on the carbs this weekend, so i'll find out i little more. as for now, i have 40 dcoe, 40 f9 & f11 emulsion tubes. car is 73. eng 81 f54 block flat top pistons. p90 head w/polished ports. stock head gasket. mallory unilite dist. msd ign & coil. stage 3 msa cam. timing is at 20deg base & 36 advanced. i'm running a carter fuel pump rated at 5psi. i see you guys are running 3psi. iguess mine is too high. i'm running my fuel through a 3 way fuel block that runs a line to each carb. no return. as far as how it runs, what i meant is, car ran like crap before i adjusted anything & exhaust smell was ok. after i made the adjustments it runs better now. runs strong at all throttle positions. it just has a slight hesitation on take off only when cold. but now the fumes is burnig my eyes badly. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted March 4, 2009 Share Posted March 4, 2009 eds240z, you've got a similar setup to mine (L28, flat top, 40DCOE, MSA cam stage 2, headers) I run 50f9, 140 main, 180 air, F11, 45 acc pump. My car is not fully tuned yet: timing are off, hesitation under heavy very suddent load, etc... but my setup works already quite well. If you have hesitation to take off I would try to play with the idle jet. I would try 50f9 and see how it goes. Do you know how many turns you've opened your idle mixture screw from bottoming? That would help you to check a rough idea to where you stand so far. If you need 50f9, you should have turned your screws at least 3 turns whereas you should target 1 to 1.5. 2eighTZ4me, the way you describe your friend's setup make me feel the car is way out. 220 for main is huge. Baseline should be: main = 4x venturi size. 220/4 = 55 which is bigger than your carb. I would go down to 180 (44x4) at least. Check also the idle, idle mixture screws are probably way out. idle jet are probably too big as well. I'm nowhere (yet!!!) a reputable weber tuner but I would suggest to consider to start tuning from scratch with a more solid setup. Main = Venturi x 4 Air = main + 50 Idle jet to get idle mixture screws turn 1 to 1.5 turn. However, I have no idea of the impact the advance on your cam could have on the setup.... Quote Link to comment Share on other sites More sharing options...
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