MECCANO Posted November 27, 2009 Share Posted November 27, 2009 I need some guidance/speculation/ insite as I’m well and truly stumped. Hopefully some can tell me why a petrol engine would run better with the vacuum advance disconnected and blocked off at the carb end. However when connected up correctly is lumpy and sounds like its running on two (i've checked the pipe for leaks and it seems to be okay). Also when adjusting the timing it seems to just make the issue worse. It’s a 2.25 petrol running an HIF SU 1.75” carb. Chris P.s Apologies, should have checked spelling before posting!!! Quote Link to comment Share on other sites More sharing options...
cipx2 Posted November 27, 2009 Share Posted November 27, 2009 This usually points to an air leak at the vacuum capsule. You checked the pipe but what about the capsule? Quote Link to comment Share on other sites More sharing options...
MECCANO Posted November 27, 2009 Author Share Posted November 27, 2009 Just ran outside and checked. When sucking on the pipe, with the other end connected to the dizzy, it holds the vacuum Quote Link to comment Share on other sites More sharing options...
cipx2 Posted November 27, 2009 Share Posted November 27, 2009 How does the engine run with the vacuum pipe disconnected but not blocked at the carb end (let it suck air in)? Quote Link to comment Share on other sites More sharing options...
MECCANO Posted November 27, 2009 Author Share Posted November 27, 2009 It runs identically to when its all connected up correctly.. so badly! Quote Link to comment Share on other sites More sharing options...
cipx2 Posted November 27, 2009 Share Posted November 27, 2009 It happened all of a sudden or did you replaced something? Any recent work or what's the history? Any other symptoms? Quote Link to comment Share on other sites More sharing options...
MECCANO Posted November 27, 2009 Author Share Posted November 27, 2009 It happened all of a sudden or did you replaced something? Any recent work or what's the history? Any other symptoms? Its a long story, i've been having problems with the weber single barrel carb for a while. It would run fine, and then out of the blue begin over fuelling and cutting out all the time. Convinced it was the carb after setting the timing spot on, this morning i fitted the HIF Su carb. Got it all running perfectly on the first test drive, was really happy with it. Parked it up and had some lunch. Came back to take it for a second run, richening it up a bit, as there was a fair amount of popping from the exhaust on over run. On the second run i got 100m before it cut out as i lifted on the approach to a junction. After several failed attempts to re-adjust the mixture i couldn't get it to start. A few times i caught but ran out of momentum. I rolled it back down the road to the house and pulled the plugs. They were dry so i presumed i had leaned it out accidently instead of richening. I gradually richened it up until i could find the point at which it ran the best (the best of which sounded like it was running on two. I thought it could be an air leak so i checked all the lines, ceonnections etc. I even replaced the o-ring on the mixture needle to check i hadn't destroyed it winding in and out repeatidly. It was then i discovered the vaccuum advance trick. Quote Link to comment Share on other sites More sharing options...
SteveRK Posted November 27, 2009 Share Posted November 27, 2009 Check that the fuel pump is delivering enough pressure & fuel - Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted November 27, 2009 Share Posted November 27, 2009 Cap off the dizzy and suck on the vac tube going to it, watch the base plate and the spring on the points -the movement can often make the spring touch the dizzy body shorting it out, and therefore no spark.... Had it a few times Fix is to fit the points properly! Quote Link to comment Share on other sites More sharing options...
MECCANO Posted November 27, 2009 Author Share Posted November 27, 2009 Cheers guys Steve, i did check the pump over by running the pipe into a bottle. It seemed to deliver at a fair old rate. I can also screw richen the mixture enough to make it over fuel considerably ( when its running properly) so i'm hoping the pump isn't an issue. It was replaced only a little while ago. Bowie cheers, will have to give that a go in the morning. will report back then! Quote Link to comment Share on other sites More sharing options...
MECCANO Posted November 28, 2009 Author Share Posted November 28, 2009 *UPDATE* just tookt he cap off the dizzy and did as bowie suggested. I couldn't see that the points where contacting with the body of the dizzy but i had just missed it. I put it through a few swings of the vacuum advance taking it up and down and put the cap back on. It fired and after blowing out the built up un burnt fuel idled happily. It runs fine until you take it up the rev range and let it drop to idle. It seems to bog the engine down, (which i presume is over fueling) to the point its trying to back fire out of the carb. I'm going to reset the timing and see where to go from there. Quote Link to comment Share on other sites More sharing options...
mobyone Posted November 28, 2009 Share Posted November 28, 2009 backfirong through carb sounds like over fueling. can you not retard/advance the ignition by twisting the dizzy? make a mark first on dizzy so you have a datum and play with it from there. also, do you not set the timing with a timing gun and remove the vacuum advance whilst doing this? i am pretty sure you do. if you did not do this when you set the timing, then i am guessing that the advance is too much already. have a play you will not go far wrong by moving the dizzy by say 7 degrees each way. too much advance is also a classic sneeze through the carb as the vanves are not closd before ignition... richard Quote Link to comment Share on other sites More sharing options...
MECCANO Posted November 28, 2009 Author Share Posted November 28, 2009 Well i had it running spot on, after i had reset the timing using the light. Then i switched the engine off to remove the timing light. Tried to start again and nothing... completely Snafu. Didn't even attempt to catch, or hicup. Pants!!! Quote Link to comment Share on other sites More sharing options...
rusty_wingnut Posted November 28, 2009 Share Posted November 28, 2009 earth wire on the distributor has a break in it. Quote Link to comment Share on other sites More sharing options...
TD5 power Posted November 28, 2009 Share Posted November 28, 2009 hi how long has the petrol been in the tank? May be worth trying to run it out a can of known good fuel just to try it, ive got an old tractor that is very picky over fuel quality. When the fuels gone off, i believe it takes on loads of water as its quite a large metal tank with not a lot of fuel in it, it makes no attempt to run but flush the system and put some fresh in there and she'll fire straight up. good luck finding the problem matt Quote Link to comment Share on other sites More sharing options...
MECCANO Posted November 30, 2009 Author Share Posted November 30, 2009 Cheers again for the suggestions guy. I checked the earth, and that seems to be all okay. The fuel is only about a week old (since filling up) I beginning to suspect the carb. I will have to strip it down and see. Will report back! Quote Link to comment Share on other sites More sharing options...
markyboy Posted November 30, 2009 Share Posted November 30, 2009 Cheers again for the suggestions guy. I checked the earth, and that seems to be all okay. The fuel is only about a week old (since filling up) I beginning to suspect the carb. I will have to strip it down and see. Will report back! Condensor? Quote Link to comment Share on other sites More sharing options...
MECCANO Posted November 30, 2009 Author Share Posted November 30, 2009 Condensor? Will give it a try Quote Link to comment Share on other sites More sharing options...
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