durty Posted April 8, 2014 Share Posted April 8, 2014 Having issues with the carb on my car and these things are black magic to me. Issue is it will start and idle fine and drive fine for a while then will randomly stop revving over 3000rpm and if I take foot off gas revs will crash and stall. Getting under the bonnet and moving the accelerator from that end then restarting the car seems to sort it for a while. Just started happening again and decided to have a look, when revving it the piston inside doesnt move at all and the revs barely climb at all, If I lift the piston as I twist the throttle then it revs out perfectly and seems fine. The carb on it is a replacement as the original one was doing the exact same thing so I replaced it. The current carb has been fine for about 4 or 5 months and has started doing this in the last week or so Dashpot has oil in it Any Ideas? Quote Link to comment Share on other sites More sharing options...
Beaver Posted April 8, 2014 Share Posted April 8, 2014 The piston will probably be jamming/sticking. Pull it apart and clean it all up and check it slides freely. The oil just dampens the piston so it doesn't flutter and go wild so unless you are running oil that is waaaaaaaaaaaaaay to heavy it shouldn't be related. That fact that two carbs have done it might just be coincidence or perhaps something else but cant think of anything which would cause it on different carbs. Ive played with them a fair bit, happy to come have a look if you want. Quote Link to comment Share on other sites More sharing options...
durty Posted April 8, 2014 Author Share Posted April 8, 2014 Comparing the original to the current one it definitely seems like the piston is sticking. Moves sort of freely but has way more resistance to it. May chuck the original back on and see how that goes Quote Link to comment Share on other sites More sharing options...
Beaver Posted April 8, 2014 Share Posted April 8, 2014 seriously pull it apart man, its 4 screws on the top and then the top lifts off and you can pull out the piston (with the needle attached) and the spring. give everything a blast with degreaser and give he piston a quick sand/scrub with the scotchbrite. Also check the black rubber diaphragm (attached to the piston) these often tear and it wont hold the pressure to make it lift properly) Quote Link to comment Share on other sites More sharing options...
durty Posted April 8, 2014 Author Share Posted April 8, 2014 Thanks man. Just pulled the original one apart and way more simple than I was thinking. Have cleaned off the piston etc and may just swap it into the other carb unless that is a bad idea Quote Link to comment Share on other sites More sharing options...
tortron Posted April 8, 2014 Share Posted April 8, 2014 if you have one apart, check that the piston drops correctly when the jet is removed. may be a bent needle/jet isnt centered. clean it first, old fuel turns to varnish and sticks everything together Quote Link to comment Share on other sites More sharing options...
durty Posted April 8, 2014 Author Share Posted April 8, 2014 Cool, cleaned up the piston from the old carb and swapped into the current carb and its like night and day, feels so much more grunty and revs out nicely. can actually see on the old piston where it has been sticking, will probably strip the carb down and give it a decent clean over the weekend. Only issue that it has now is if you rev it and then let off the accelerator it drops smoothly to 2000 rpm then hesitates there for a second before dropping to idle, not a big deal though. can drive it tomorrow. Also, the stupid screws that hold the top cover on are made of the softest metal, had to take the vice grips to a couple Quote Link to comment Share on other sites More sharing options...
Beaver Posted April 8, 2014 Share Posted April 8, 2014 yeh the screws fuck out easy. Go to a fastner shop and get some bling cap screws. will cost like 5 bucks. re: odd idle, just recheck everything is smooth and not sticking Quote Link to comment Share on other sites More sharing options...
KKtrips Posted April 8, 2014 Share Posted April 8, 2014 When reassembling it then make sure that the diaphragm is located in the correct place too. There is a rubber dowel (for lack of a better word) around the rim of the diaphragm that slots into a recess in the body of the carb. Quote Link to comment Share on other sites More sharing options...
durty Posted April 8, 2014 Author Share Posted April 8, 2014 Yup yup, saw that and got that the right way Not as complicated as I thought when I first looked at it Quote Link to comment Share on other sites More sharing options...
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