We made it back from Cornwall the other week, complete with a bodged carb mechanism. I have put a replacement throttle lever on and readjusted the the throttle link that I had to move a little when it broke. Now the engine is running rough and shaking a bit more than normal. I thought it may be down a cylinder so I started pulling off plug leads to check. Both the LH cylinders caused the engine to stall when I pulled the leads and both the RH cylinders, well I couldn't really tell the difference leads on or off. I took these 2 plugs out and they looked ok and when plugged in the lead they showed a spark. Any ideas or suggestions more than welcome. I've reached the limit of my knowledge :- Thanks.
One or more of your valve gaps has closed up. It got hot enough for a valve seat to come loose and start to tap it's way into the head. Very common. In my experience often due to a leak in the servo vac pipes somewhere causing it to run lean. I just scrapped a heap of T4 heads like that, but you can have them re-seated. Or the throttle linkage has come loose and carbs are out of balance.
Thanks for the reply Zed.....finger crossed for the first option. The heads and engine are low mileage and there is no servo vac pipe.
I have been fiddling with the linkage because of the temporary fix the other week. I haven't touched idles or mixtures, only the actual linkage. Could this be my problem?
Timing over-advanced then. A few degs makes a whole lot of difference. Just a thought. I hope the carb linkage has rattle loose. If you have standard carbs also check all the wires are tight.
What did you do? Have a look and if a carb isn't returning to the stop adust the linkage so they both hit/leave the stop at the same time when operated via the cable arm. That's best you can do by eye, and if the stops have been kept in sync is probably nigh on spot on.
you could also start her and either feel the manifolds or put hand near the exhaust where it exits each cyinder to see if each cylinder is firing (but becarefull as they will get hot ) what linkage are you using , and what is the og dell spindle ? when i did mine i made up some stainless arms so you can fine adjust on the carbadjusting screw and not constantly messing with the linkage . the CB stuff was real bad stuff hope this helps
I see these aren't stock carbs so my knowledge is limited but if your carbs are unbalanced so that one butterfly is open more than the other the engine will run just as you describe so it'll sound like one side of the engine is misfiring. Pull some of the plug leads and you might think that cylinder is not firing at all. It's best adjusted with a carb balancer which compares the suction on each carb. You then adjust so both are equal.
Update: I started from scratch and took all the plugs out, one came out with helicoil attached. Then compression tested . Readings were No.1 130psi No.2 135psi No.4 142psi No.3 no reading Then changed 3 plugs for new and cleaned the one with the coil attached.(will fit a new one asap) The old ones all looked ok, brown and dry. Fitted new HT leads and distributor cap. Got it fired up and let it run for a while and it sounded better than yesterday but not as good as it has been. Then had another go at the linkage, it's difficult to watch both carbs at the same time! I had trouble deciding what was spot on, so I gave it some revs, probably about 2000rpm and adjusted the linkage until it sounded nice and smooth. When I dropped the revs back to tickover it sounded a lot better. This is about as good as I can get it. Now I'm much happier than yesterday, I still tried pulling the HT leads off in turn and strangely removing either 4 or 3 stalled the engine almost immediately and pulling 1 or 2 changed the engine note, but it was happy to run without one of these cylinders. This bit is still a mystery. Thanks for all your comments and advice. I should still probably check the valve clearances, but the last time I did this I failed and had to get help. :-[ This could be one for you Zed, seeing as your back in business now.
Dude, you need to get an air flow meter you use it to set the carbs throttle stops (linkage disconnected) then you sync the linkage to the carbs
heat cycling can throw freshly installed carbs out... doing the basic set up always is going to get the most out of your mpg too
