250 Monza idle problems

[email protected] · Post by **[email protected]** » Thu May 26, 2011 6:58 am

66 Monza with a poor erratic idle and eventual stalling. I can not seem to get idle settings right. puffs through the exhaust and occasional puffs back through the carb. I performed a leak down test and at 80 lbs. had 70 lbs. showing with some ring blow by and a little through the exhaust valve. I regret now having taken the head off and lapping the valves in with compound as it is now worse. Valves remounted are probably in different positions. The exhaust valve is cupped and pitted. Intake valve looked pretty good. I did not have the proper 8mm New Way pilot so I could not touch up the seats. I do not think that the exhaust valve has enough material to reface it.
Are these idle symptoms consistent with a mediocre valve seal?

[email protected] · Post by **[email protected]** » Thu May 26, 2011 8:59 am

Started thinking about my half a--ed valve job and decided to double check my valve clearances since it seemed to rum better cold than warm. Exhaust seemed tight. I had set it as a snug .003'. Adjusted to .004". Its much happier than before. Any suggestions for an old motor valve clearance?

bobnorton · Post by **bobnorton** » Thu May 26, 2011 9:57 pm

A couple of thou more wont hurt and ground valves settle in anyway,too much ignition advance?.

[email protected] · Post by **[email protected]** » Fri May 27, 2011 4:59 am

advance is right in the 5-8 degree range.
I am going to set both int and exh. at .005 and see how it goes

bobnorton · Post by **bobnorton** » Fri May 27, 2011 9:14 am

I usually test seats by pouring petrol down the port and waiting to see how long till it seeps past the valve ,30 secs is ok.Valve timing ok? Easy to get it wrong .

[email protected] · Post by **[email protected]** » Sun May 29, 2011 7:51 am

Did not do the petrol test and its all assembled now. The leak down test looked and sounded good even though the seats and valves did not look that great.
I re-checked valve and crank timing marks and they all lined up....sort of. Looks to be a pretty casual affair on Ducati's part. I did not do valve timing with the degree wheel so I may need to do that as a double check. The manual I have makes me think it started out in Italian and was translated by someone who speaks english as a third or fourth language and not very well.

[email protected] · Post by **[email protected]** » Wed Jun 01, 2011 7:23 pm

Checked cam timing with the degree wheel and it is right on. In the past it had run a little better on an Amal concentric M1 carb instead of the stock Delorto. Not now it still is erratic and stalls with frequent carb farts. Not really a backfire through the carb but a puff. I am at a loss on what I have missed. Any ideas would be appreciated.

bobnorton · Post by **bobnorton** » Thu Jun 02, 2011 10:28 am

I take it that you know that you have to rotate the motor a number of times before all the cam markings line up,and check that the points are breaking, some of the markings are not easy to spot.

[email protected] · Post by **[email protected]** » Thu Jun 02, 2011 8:19 pm

Yes, been there a few times. One of the cam bevel drive gears has its mark hidden/masked by the lock tab washer so I am very careful there. I got some understandable cam timing degree wheel numbers on-line that corresponded with what I found on my engine. I have been very careful with ignition timing. Separate checks have been in agreement. I set TDC with a spark plug hole piston stop and a degree wheel with equal degree amounts on either side of TDC.
When I did the leak down test I was able to get the engine to stay at TDC with 80 lbs. of air pressure going into the cylinder whenever I got it EXACTLY at TDC which was very close to the degree wheel read out. If it was just a fraction off the engine turned one way or the other.
The valves and seats are not great, especially the exhaust, but on the leak down test it held 78 lbs with 80 lbs going in. Really not bad at all. My question there is does it seal that well every cycle.
It has stock points and condenser that are old but with .015 clearance the timing when set at 5-8 degrees BTDC is towards the end of the adjustment slot but not all the way. Can a marginal condenser give odd idle characteristics? I always thought condensers were either altogether bad or OK.
I have two different carbs, the stock Delorto and an Amal concentric M1. Both have similar idle characteristics. The Amal sits at the angle of the intake port which probably is not ideal. It has a plastic float with a tab cast into it for the float valve. It has become bent from sitting so long with the weight of the float pushing the valve open. I have pushed it straight. Does not seem to help.
Argh!

bobnorton · Post by **bobnorton** » Thu Jun 02, 2011 8:59 pm

To cheer you up ,it took about 4 years of fiddling to get my 250 to run acceptably.Hotwire the ignition system to see if the problem goes away.

[email protected] · Post by **[email protected]** » Fri Jun 03, 2011 8:51 pm

Hotwire ignition system?

bobnorton · Post by **bobnorton** » Sat Jun 04, 2011 7:37 am

Hotwire---run a temporary wire from the live battery terminal to the ignition coil terminal --the one that does not go to the points, try the bike,if the problems gone then you need to check the electrics as you have a bad connection,switch or wiring, its one way to eliminate a lot of the possibles.