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Trying to get my brothers 1600 CVH running properly is proving a nightmare! It's only firing on two cylinders. There's a nice fat spark from each of the plug leads, the plugs are new and gapped properly, so I don't reckon it's electrical. It's cylinders 1 and 2 that're not playing ball, so my suspicion lies with the carb (it has twin 40 Dell'Ortos). Thing is, both carbs are jetted exactly the same, but when I take a look at the plugs on cyls 1 + 2 they're wet  . I thought it could be too much / too little fuel pressure so I disconnected the fuel pump and ran the engine on what was in the float chambers: same problem. I'm a bit baffled now - anyone got any ideas / tips on adjusting twin 40's? |
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Trying to get my brothers 1600 CVH running properly is proving a nightmare! It's only firing on two cylinders. There's a nice fat spark from each of the plug leads, the plugs are new and gapped properly, so I don't reckon it's electrical. It's cylinders 1 and 2 that're not playing ball, so my suspicion lies with the carb (it has twin 40 Dell'Ortos). Thing is, both carbs are jetted exactly the same, but when I take a look at the plugs on cyls 1 + 2 they're wet . I thought it could be too much / too little fuel pressure so I disconnected the fuel pump and ran the engine on what was in the float chambers: same problem. I'm a bit baffled now - anyone got any ideas / tips on adjusting twin 40's? If the plugs are wet all that it's telling you is that there is fuel but no combustion, but you knew that anyway. Not an expert on webers, but my first port of call would be the float valve. I know it's a PITA, but what you need to do is isolate the problem. Try swapping the carbs round if possible, if the problem moves to 3 & 4 it's the carb. If it stays with 1 & 2 then it isn't. I've lost count of the number of people (me included) who have been sure that the problem lies with one particular component and spent ages fiddling with that part, right down to replacing it with a new unit before finally realising that the problem was somewhere else altogether. |
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if you havent tried already, please do a compression check it might not be that, but you never know what it could be.
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I'm dressed in black again until someone invents a darker colour.
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if you havent tried already, please do a compression check it might not be that, but you never know what it could be. Just what I was going to suggest. Will at least tell you if it's the bottom or the top causing the trouble. Swap carbs is another good idea too. My mate was having trouble with a 95% project car he was assembling with twin carbs & was messing about with everything like you & in the end we swapped the twins for the original twin-choke [that came with the project anyway] & it fired straight away  |
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They're right, do a compression check, in the worst case scenario you're valves could be in pretty bad shape, with any luck it's just a case of a dodgy carb that can be changed or fixed.
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"He's not the messiah, he's a very naughty boy!"
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Thanks for the sound advice (as always!  . Will try a compression test although the engine was completely rebuilt not long ago - but then again that's no guarantee that things are OK is it?  It's always difficult working on things that someone else has done! He isn't around to ask at the minute either... After the comp test I guess it'll be swapping the carbs over but, yeah, that is a bit of a faff. Having said that I think the original carb and manifold is lying around somewhere so it might be worth bolting that up and seeing if it fires on all four. Runs surprisingly OK on two pots, but it isn't under any load! I have to be careful when I fire the thing up cos it's pretty loud and the neighbours get a bit hacked off! Thanks again for the feedback chaps  |
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Had another thought that relates to Revs' post & that's not just the valves but the hydrulic tappets playing up. ....But seeing as though it's been rebuilt, should be OK. Presume the oils nice & clean-ish - it's not lumpy or too gungey. Bought a XR3i for the missus a few years back that had been standing & it was mint [ish] & factory standard but was gunged-to-hell. It kept losing oil pressure as the oil pick-up pipe was gunged solid!!!!!   |
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I lost a cylinder on the sunbeam some time back. Turns out the last retard to service it for me had advanced the timing so far that it melted a nice hole in the no.1 piston. Hope your problem isnt as bad as that.
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Another thought. What are the plugs actually wet with when you take them out? I've assumed it's petrol, but what if it's oil or coolant? If it is then you could be dealing with something more serious than a carb problem. Rings? Gasket?
Worked on a mini once that wouldn't fire. Some eejit had connected the petrol pipe to the carbs overflow and the overflow where the petrol pipe should be. Instant and major flooding. Could have kicked myself for not spotting it straight away.
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I'm pretty sure it's petrol the plugs are soaked in. I'll have to check ignition timing but that would affect all 4 cylinders I'd have thought. It just seems a bit odd that it's cylinders 1 and 2 that are out - the ones fed by one of the carbs. It could of course be a gasket problem thats blowing between these two cylinders.... a compression check will fathom that out, but I have to get a compression tester first . Funnily enough it does spit back through that carb sometimes, so there is ignition taking place occasionally. Haven't really got time to spend on it at present but my brother was hoping to have it ready for RCS this year. |
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. I thought it could be too much / too little fuel pressure so I disconnected the fuel pump and ran the engine on what was in the float chambers: same problem.
. Will try a compression test although the engine was completely rebuilt not long ago - but then again that's no guarantee that things are OK is it? 
