Yes I'll do that as I'm doing the tappets tomorrow.
ET: Engine (Twin) Help needed.
- Thread starter Chris Launders
- Start date
I Imagine that there will be leakage down the valve guides. How does that affect the testing of the valve seats?
have you pulled the plugs, maaybe running super lean?
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
Vic
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.
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.
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
Vic
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
An update on the problems.
Getting nowhere with the Mk1s because of very worn slides and at around £45 EACH not wanting to buy new just to try them out I refitted the Mikuni's, first problem one of the choke plunger parts was missing (1 into 2 cable chokes) so ordered a new one.
When this came I noticed it had a weaker spring than the existing one but other than that was right.
So setting these with the slides fully down and opening together I then screwed the throttle stops in equally until it would tick over nicely and took it for a spin up the road. within 200 yards it started missing on the front cylinder and this got progressively worse in the next 200 yards until it was only running on the rear cylinder.
I took the front float bowl off thinking it may be fuel starvation (I had turned the fuel off straight away to check this) but it was full.
I then started on the ignition for the front cylinder thinking something may be breaking down, so made and fitted a new copper cored HT lead (the exiting one was a decades old silicon car lead), try again and no change, next I changed the condenser, try again, no change, but this time when I turned round to come back there road was empty so opened it up more and it then picked back up on the front cylinder. this then led be to think it was possibly flooding the front carb (but not enough to overflow), or excessively rich, so decided the next day I would swap the carbs over.
Before I got round to this the I remembered the weaker choke spring mentioned earlier along with the fact I had changed from a Manx tank to a modified Dommi tank so I swapped the choke assemblies over and rerouted the cables so the junction box was below anywhere the tank could interfere with it.
SUCCESS, it now ran reasonably well, enough for me to know I had solved that issue, I've now balanced the carbs with vacuum gauges and it is almost right, I had no spare new plugs so ordered some and once I have made a new throttle cable for the front carb I will set about final tuning.
So it was either the weaker choke spring or/and the tank interfering with the cable junction box meaning the front cylinder choke was always on. None of this explains why I have always had trouble as I only swapped the tank and carbs over this winter, probably just my incompetence.
Chris
Getting nowhere with the Mk1s because of very worn slides and at around £45 EACH not wanting to buy new just to try them out I refitted the Mikuni's, first problem one of the choke plunger parts was missing (1 into 2 cable chokes) so ordered a new one.
When this came I noticed it had a weaker spring than the existing one but other than that was right.
So setting these with the slides fully down and opening together I then screwed the throttle stops in equally until it would tick over nicely and took it for a spin up the road. within 200 yards it started missing on the front cylinder and this got progressively worse in the next 200 yards until it was only running on the rear cylinder.
I took the front float bowl off thinking it may be fuel starvation (I had turned the fuel off straight away to check this) but it was full.
I then started on the ignition for the front cylinder thinking something may be breaking down, so made and fitted a new copper cored HT lead (the exiting one was a decades old silicon car lead), try again and no change, next I changed the condenser, try again, no change, but this time when I turned round to come back there road was empty so opened it up more and it then picked back up on the front cylinder. this then led be to think it was possibly flooding the front carb (but not enough to overflow), or excessively rich, so decided the next day I would swap the carbs over.
Before I got round to this the I remembered the weaker choke spring mentioned earlier along with the fact I had changed from a Manx tank to a modified Dommi tank so I swapped the choke assemblies over and rerouted the cables so the junction box was below anywhere the tank could interfere with it.
SUCCESS, it now ran reasonably well, enough for me to know I had solved that issue, I've now balanced the carbs with vacuum gauges and it is almost right, I had no spare new plugs so ordered some and once I have made a new throttle cable for the front carb I will set about final tuning.
So it was either the weaker choke spring or/and the tank interfering with the cable junction box meaning the front cylinder choke was always on. None of this explains why I have always had trouble as I only swapped the tank and carbs over this winter, probably just my incompetence.
Chris
Chris, How does the front carby clear the rear head and/or top frame rail........I've found the only carb that will clear both is the Mk 1 concentrics with custom made manifolds.......I've seen carbs positioned under the rail with an up draft manifold........not ideal as they tend to "pool up" with fuel on the overrun.