ET: Engine (Twin) Help needed.

[Chris Launders]

Ok, I'm getting really really desperate.
I built a Norvin 30 years ago, and I have been trying to get it to run something like decent since then. Maughans rebuilt the chopped engine with 7.3 pistons and Mk2 cams and it runs a Norton box and belt primary with a crank mounted Lucas 3 phase alternator.

I've had Amal Mk2s, Mikuni's and now Amal Mk1s on it, it's had twin points with twin plug ignition with standard ATD, twin points with HD ATD single plug ignition and now twin points standard ATD single plugs

And I've never been able to get it to run right, for instance I just had it ticking over smoothly, set off up the road, and it won't shut off properly, instead of sort f 800 rpm it's running at 2.000, it's always pulled well but never shut off properly whatever I've done and never ticked over again reliably once I've got right to begin with.

By the way I have no problems sorting my "Shadowish" or any of the other bikes I have.

I don't want to fit a Lucas magneto even though I have a good one because the engine only turns over slowly because of the box/primary ratio and I'm reluctant to try electronic ignition and a BTH is expensive just to try.

Any ideas please

Chris.

 

[timetraveller]

Have you tried running it with a Colourtune in each plug hole? If you can get it warmed up and then put the Colourtunes in, put it in gear with the rear wheel off the ground and then using the rear brake let is run against some resistance. Looking through the Colourtunes will show you whether it is misfiring, the fuel feed is erratic or whatever. It is a poor mans rolling road but for a few seconds at a time will work. Good luck.

 

[brian gains]

you've tried all the obvious stuff, air leaks, sticking cables. I had a similar issue but just from start up, the cable ferrule was hanging up on the carb' cap adjuster, cack handed assembly.

 

[Chris Launders]

Have you tried running it with a Colourtune in each plug hole? If you can get it warmed up and then put the Colourtunes in, put it in gear with the rear wheel off the ground and then using the rear brake let is run against some resistance. Looking through the Colourtunes will show you whether it is misfiring, the fuel feed is erratic or whatever. It is a poor mans rolling road but for a few seconds at a time will work. Good luck.

I've not had them in this time (just fitted the Mk1s) and I don't have a centre stand to have the back wheel off the ground. The carbs shouldn't be far out, I have the same settings as my "Shadowish"

 

[Chris Launders]

you've tried all the obvious stuff, air leaks, sticking cables. I had a similar issue but just from start up, the cable ferrule was hanging up on the carb' cap adjuster, cack handed assembly.

The carbs are not hanging up at all, dropping straight back to the stops. it has been the same with the Mikuni's I took off, new cables and evrything.

 

[oexing]

Some say when valves got no clearance in hot engine it will have high revs in idle. Maybe check valves for knowing all is right ?

Vic

 

[Chris Launders]

I'll do that.

 

[Cyborg]

I would be tempted to do a vacuum test on the intakes. Remove carb, bolt on adapter plate draw a vacuum with the intake valve closed and see if it holds. Maybe someone went to town on the intake porting at some point. Does it use 2 front heads or does it still have the rear?

 

[Chris Launders]

I would be tempted to do a vacuum test on the intakes. Remove carb, bolt on adapter plate draw a vacuum with the intake valve closed and see if it holds. Maybe someone went to town on the intake porting at some point. Does it use 2 front heads or does it still have the rear?

Front and rear, 33mm. (the front was ported when I got it), I had the rear matched to it.

 

[Cyborg]

It’s a long shot and not likely to cause what you are experiencing , but I’d still be tempted to check, especially the rear head.