ET: Engine (Twin) Help needed.

[Chris Launders]

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.

Yes I'll do that as I'm doing the tappets tomorrow.

 

[timetraveller]

I Imagine that there will be leakage down the valve guides. How does that affect the testing of the valve seats?

 

[brian gains]

have you pulled the plugs, maaybe running super lean?

 

[oexing]

Vacuum test - I don´t know. Common is a pressure test by having an air hose adapter in the spark plug place. When you hear some hissing at the carb intake, it is the intake valve. When hissing is at the exhaust pipe, it is exhaust valve. When hissing is from the engine case, like at the adjuster inspection cap, it is the piston rings.

Vic

 

[Chris Launders]

have you pulled the plugs, maaybe running super lean?

The rear is black sooty and the front black shiny. But I've literally only just got it running on the Mk1s and been about 1/4 mile, but whatever I've done it's not been anything like usable.

 

[Cyborg]

I Imagine that there will be leakage down the valve guides. How does that affect the testing of the valve seats?

Good point. I install valve seals, so not an issue. Personally I would still do the test. I would be tempted to use a leak detecting dye sprayed around the outside of the port and see if any shows up on the port wall. As mentioned previously, it’s a long shot, but after living with it for that long, I’d try just about anything.

Oexing… pressurizing the combustion chamber won’t tell you if the engine is sucking air through the port wall. According to legend, rear heads can’t be ported as much as front ones and some folks have gone too far.
Vacuum testing heads is a relatively common practice at cylinder head rebuilding shops.

 

[oexing]

Vacuum testing common - less so than leak testing I´d think. When porting a head the mech should notice at once when he overdid it into free air. This may happen but more often some valve will not seat properly so then the pressure test will show, certainly not useful for bad porting jobs , yes.

Vic

 

[erik]

When I rebuilt My Rapide engine I‘ve got. two Sporty Magacycle camshafts. After the rebuilt the bike was Not running well. Working on the carbs had no real effect. Tickover although very bad.I tried everything including new timing of the cams. It was very frustrating! Then I took the original camshafts which came with bike and a wonder happened! The carbs where easy to tune and the Engine was running as I expected it should! Be patient you will get your bike running! Best regards Erik