Beaver Posted May 4, 2015 Share Posted May 4, 2015 Right, Im trying to sort out why the engine in my 120y is running like crap. Its an a15 which I have never had running right. State of play: Generally easy to start, pretty much first pop when warm. Very rough idle (wont idle below about 1000rpm, smooths up about 1700-2000rpm) Giving it the boot it runs great and seems to pull as it should Has low vacuum at idle (about 10 in/hg, the a15 in my van pulls a bit over 20 in/hg at idle which is where the gauge says it should be at idle, it runs like a treat) I have tried three different carbs on in, and it pretty much runs the same. One carb I know is a good runner as I used in on my old a12 motor which ran like a sewing machine. I rebuilt this carb not that long ago as well. The carb I tried most recently can be stalled out with the idle mixture adjustment wound right in, which suggests there is no large air leak. I could not do this on the carb that came with the motor (cant recall if I could do it on the rebuilt carb from my a12) I have tried two different manifolds on it, runs the same. I have replaced the manifold gasket, runs the same. If I introduce a big vacuum leak (ie take out one of the bung plugs in the manifold) it makes very little difference to how it runs. I have tried the brake clean around all the joints trick, no success in finding a leak. I have replaced all the ignition system apart from the coil. This is on the next to try list. I have a points replacement kit, but also tried the points again, and a different dizzy. No change. I have done a compression test, was about 150 on all 4. I have checked and set the vale clearances. I have checked and set timing to factory. Basically Im wanting to make sure Im not missing anything which could be giving me these issues, or some encouragement that it may be a lowly coil causing my issues. Cheers Quote Link to comment Share on other sites More sharing options...
cletus Posted May 4, 2015 Share Posted May 4, 2015 cam is stock? booster has vac leak? pcv system working correctly? 1 Quote Link to comment Share on other sites More sharing options...
Goat Posted May 4, 2015 Share Posted May 4, 2015 Maybe something ham like a leak on an intake valve stem? Pull head and swap it for your spare one? If that even fits and if you even have a spare head... Hah Quote Link to comment Share on other sites More sharing options...
AllTorque Posted May 4, 2015 Share Posted May 4, 2015 What's the compression values on the van motor? Would be interesting to compare. Have you tried blanking off the vacuum hose to the brake booster or clamping off other vacuum lines and seeing if vacuum increases at the gauge? 1 Quote Link to comment Share on other sites More sharing options...
Beaver Posted May 4, 2015 Author Share Posted May 4, 2015 cam is stock? booster has vac leak? pcv system working correctly? No idea on cam.....no reason to believe its not stock, but then again the seller didnt know much about the engine. I have wondered about this though.... No booster. PCV system is just a valve on the manifold, which appears to operate as it should (ie it holds vacuum in one direction). I have also tried it with this blanked off, no change. Quote Link to comment Share on other sites More sharing options...
Beaver Posted May 4, 2015 Author Share Posted May 4, 2015 Maybe something ham like a leak on an intake valve stem? Pull head and swap it for your spare one? If that even fits and if you even have a spare head... Hah Wouldn't that show up on comp test tho? As in if its not holding vacuum, it wouldnt hold compression? Nah only have a12 head which is fucked. 1 Quote Link to comment Share on other sites More sharing options...
Seedy Al Posted May 4, 2015 Share Posted May 4, 2015 in the event you pull head off I can vac test etc but that's not much handy Quote Link to comment Share on other sites More sharing options...
Yowzer Posted May 4, 2015 Share Posted May 4, 2015 Have you checked your cam timing? 2 Quote Link to comment Share on other sites More sharing options...
Beaver Posted May 4, 2015 Author Share Posted May 4, 2015 What's the compression values on the van motor? Would be interesting to compare. Have you tried blanking off the vacuum hose to the brake booster or clamping off other vacuum lines and seeing if vacuum increases at the gauge? Havnt done the van, will have a crack tho and see what they are like. As above, no booster, only vac line is to the dizzy. Pretty sure it didn't make a difference with it block but will check. Dizzy holds vacuum fine and hose is in good nick so doubt its an issue. 1 Quote Link to comment Share on other sites More sharing options...
Goat Posted May 4, 2015 Share Posted May 4, 2015 Nay, as the leak would be in the intake not it the combustion chamber. I mean it's sucking in air from around the valve. Worn valve guides. So you have a vacuum leak there. Just a suggestion. Not sure how you would diagnose that. Quote Link to comment Share on other sites More sharing options...
Beaver Posted May 4, 2015 Author Share Posted May 4, 2015 Have you checked your cam timing? Negative/not really sure what that means. Sounds like maths is involved.....ill google it Quote Link to comment Share on other sites More sharing options...
Yowzer Posted May 4, 2015 Share Posted May 4, 2015 Here's a thing 1 Quote Link to comment Share on other sites More sharing options...
Yowzer Posted May 4, 2015 Share Posted May 4, 2015 If your camshaft is out a tooth / your chain is excessively worn out then the valve opening / closing times will be all up the shitter causing symptoms similar to your discription. Worth a check since you ain't found nothing else yet Quote Link to comment Share on other sites More sharing options...
piazzanoob Posted May 4, 2015 Share Posted May 4, 2015 The running rough side of things is sometimes a symptom of a blown head gasket perhaps try a teekay test to see if it has or not. Quote Link to comment Share on other sites More sharing options...
Beaver Posted May 4, 2015 Author Share Posted May 4, 2015 If your camshaft is out a tooth / your chain is excessively worn out then the valve opening / closing times will be all up the shitter causing symptoms similar to your discription. Worth a check since you ain't found nothing else yet Cheers, seems straight forward to check. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted May 4, 2015 Share Posted May 4, 2015 be sure to count the links. That's the critical part of the equation. it could have a cam too. I bought a used motor with a cam once. It idled like a bag of dicks, and made very little vaccuum. If it does, pop the oil cap on your Van, and wind the motor over while looking into the rocker cover with a torch. Do the same on your motor. If you've got a cam, you'll see it'll have a lot more lift. When i bought the above motor, (as a bit of an unknown) I wound it round, and was like faaark when I saw how far the valves opened. 1 Quote Link to comment Share on other sites More sharing options...
AllTorque Posted May 4, 2015 Share Posted May 4, 2015 I really hope that is your problem. That would be cool. 1 Quote Link to comment Share on other sites More sharing options...
Popular Post cletus Posted May 4, 2015 Popular Post Share Posted May 4, 2015 if it goes rumpa rumpa pukkata pukkata pukkata rump blump blump when its idling, then it might have a BIG CAM. science. 13 Quote Link to comment Share on other sites More sharing options...
Yowzer Posted May 4, 2015 Share Posted May 4, 2015 Add big carbs and big zorst and win at life Quote Link to comment Share on other sites More sharing options...
AllTorque Posted May 4, 2015 Share Posted May 4, 2015 Then all you need is a big motor. 1 Quote Link to comment Share on other sites More sharing options...
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