Stacov Posted August 14, 2005 Share Posted August 14, 2005 I thought i had fixed this but its come back again Every time i brake it bumps up my revs 400-500rpm and no im not touching the throttle for the brake! Even when car is out of gear u touch the brake pedal and it bumps revs up 400-500 rpm no hoses are touching or anything its got me stumped!! Quote Link to comment Share on other sites More sharing options...
atropine Posted August 14, 2005 Share Posted August 14, 2005 thats wierd shit man.. havent encountered that before sorry Quote Link to comment Share on other sites More sharing options...
Guest escort_boy Posted August 14, 2005 Share Posted August 14, 2005 maybe an erthe some where? Quote Link to comment Share on other sites More sharing options...
Snoozin Posted August 14, 2005 Share Posted August 14, 2005 Sounds to me like it could be a problem concerning the brake booster or associated hoses? (If you have a booster of course) Quote Link to comment Share on other sites More sharing options...
v3k Posted August 14, 2005 Share Posted August 14, 2005 Are you flexing the peddle box when you press the brake? It may be twisting the whole box and the throttle cable too?? Just guessing... Quote Link to comment Share on other sites More sharing options...
esky boi Posted August 14, 2005 Share Posted August 14, 2005 Hmm thats weird yea could be fouling the throttle cable as v3k said? Quote Link to comment Share on other sites More sharing options...
SYKOV6 Posted August 14, 2005 Share Posted August 14, 2005 nah its pretty simple. as you press the brake pedal the booster is sucking vacuum out of the inlet manifold causing the engine to run lean for a second. this alters the airflow through the carb thus a little more fuel =more revs. or some explaination pretty close to that it also happens on my mitsi chariot family hack and thats injected. Quote Link to comment Share on other sites More sharing options...
Defcon Posted August 14, 2005 Share Posted August 14, 2005 Check to see if any of thr brake booster hoses and fittings are loose.Bound to be the problem. My Twins backfire at the mo when I hit the brakes, sounds like pop corn, "pop pa pop pop" Carb may need a bit of tune too. Def' Quote Link to comment Share on other sites More sharing options...
Stacov Posted August 14, 2005 Author Share Posted August 14, 2005 some good ideas there yea i think its something to do with the vacuum On my day off ill recheck everything listed here also have a play with the carby just incase keep them ideas coming gotta fix this problem because if it makes the engine just lean for a second that could end up being real bad! Quote Link to comment Share on other sites More sharing options...
SYKOV6 Posted August 15, 2005 Share Posted August 15, 2005 the leaning out of the engine woulkd be very minor. prolly about the same as removing the air filter Quote Link to comment Share on other sites More sharing options...
Stacov Posted August 15, 2005 Author Share Posted August 15, 2005 well went had another play still cant find the problem checked all hoses and connections, checked pedal box etc.. it got to the point i could hold the brake down and get the revs around the 2000rpm mark crazy could this be a carby related thing / intake manifold ? oh yeah and u know how u can usually pump the brake while car is going and it goes hard for a few seconds? well it doesnt even do that while we are here anyone know the mixture screws are on a 40/40 webber? theres 2 screws at the bottom and 2 atm anyone able to tell me exactly what they are thanks Quote Link to comment Share on other sites More sharing options...
SYKOV6 Posted August 15, 2005 Share Posted August 15, 2005 does your engine have a hot cam? if so a camshaft with increased lift and duration will result in less manifold vacuum, which means ya booster wont work properly. some people put in a vac tank to save vac for the brakes as you only have enough vac at high revs with ya foot off the gas. most boosters need at least 12hg of vac to work properly at idle. get a vac guage and check it. my motor with a drag cam has less than 6 hg of vac at 1000 rpm. which is only just enough to make the carb work let alone a brake booster so i dont have one. Quote Link to comment Share on other sites More sharing options...
Stacov Posted August 15, 2005 Author Share Posted August 15, 2005 yup has a hot cam in it but its not just idle does it when u brake while slow driving too.. e.g. coming to full stop. Doesnt do it while ur doing 100 how much are one of those vac guages? and is it hard to install? Quote Link to comment Share on other sites More sharing options...
SYKOV6 Posted August 15, 2005 Share Posted August 15, 2005 best just to buy a hand held one. i paid about 50 bucks for a top quality one. they are real useful for tuning modded engines as ya just adjust the mixture until ya have the most vacuum Quote Link to comment Share on other sites More sharing options...
Stacov Posted August 15, 2005 Author Share Posted August 15, 2005 best just to buy a hand held one. i paid about 50 bucks for a top quality one. they are real useful for tuning modded engines as ya just adjust the mixture until ya have the most vacuum sweet, ill get one next time im in palmy or napier dunno when that will be. Quote Link to comment Share on other sites More sharing options...
SYKOV6 Posted August 15, 2005 Share Posted August 15, 2005 yeah they are bloody handy just plug it into a manifold port and away ya go the one that ive got also does fuel pressure as well. Quote Link to comment Share on other sites More sharing options...
Stacov Posted August 15, 2005 Author Share Posted August 15, 2005 nice, Im 100% sure it wasnt doing it the other day aye but car was running like crap so played with the carby then it started doing it again. Car running like crap again anyways specialy when u try feed it. Just doesnt have the horse power it was putting out before and just doesnt sound right as if its not getting enough fuel or something. Sounds as is missing or hitting one massive flatspot. Also finding it very hard to start the car doesnt have a autochoke never did but wasnt ever this hard to start. im thinnking might need abit more fuel so i guess ill try tune the carby again if that fails might put on a 32/36 carby as they are easier to tune then the 40/40. Quote Link to comment Share on other sites More sharing options...
SYKOV6 Posted August 15, 2005 Share Posted August 15, 2005 is that with the carb that was on it when it caught fire? did u strip it and check it out? did u check the base plate was still flat and sealing after all that heat? Quote Link to comment Share on other sites More sharing options...
Stacov Posted August 15, 2005 Author Share Posted August 15, 2005 is that with the carb that was on it when it caught fire? did u strip it and check it out? did u check the base plate was still flat and sealing after all that heat? yeah. I pulled it apart but yeah the top part, not sure what its called but was abit bent took 2 gaskets to seal it properly its the big gasket too. but seem to be working ok intill now. Might pay to try another carby ? Quote Link to comment Share on other sites More sharing options...
davidian Posted August 15, 2005 Share Posted August 15, 2005 man, i wouldnt trust any carb thats been inflamed and almost ruined ya car. id strip it down to the last screw/spring and reassemble. or go for new Quote Link to comment Share on other sites More sharing options...
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