Tracking down an air leak

[sideout]

Hi
I've been trying to adjust the jetting on a newly rebuilt SIL 200 with a (previously working) Jetex carb running through the air box.
The mixture screw has little effect and to make it run at all the throttle needs to be open a little bit more than it should. When blipping the throttle it takes a while to return to idle, so I reckon its weak at the idle jet stage.

Are there any tricks or tips for tracking down an air leak? I was going to spray easy start around the joints to see if the revs increase, but it might be tricky with forced air cooling

I really want to eliminate the mag side oil seal, so if any one knows of a way before I strip it down and replace it I'd be grateful to hear it

Cheers,

Nigel

[Dazza]

Never done it myself but I believe you set the engine to a fast tickover and then spray plus gas or similar around where you'd normally expect a leak and see if the revs rise significantly

[sideout]

Never done it myself but I believe you set the engine to a fast tickover and then spray plus gas or similar around where you'd normally expect a leak and see if the revs rise significantly

Yeah, that's what I've done on a car before now Dazza, picked up an air leak on an inlet manifold, but...... I was thinking the fan would blow the stuff all around the cowl so it might not be clear which of the base gasket, inlet, exhaust or head was leaking.
I'll give it a go any way tomorrow if I get a chance and report back

[starreem]

Your revs will go down, not up spraying starter fuel or whatever, when you find your airleak.

[WINTERMODEL150]

Hi,put a 48 pilot jet in the carb instead of the 45 and give it a good clean out first ,then spay some wd40 or carb cleaner around the intake area but be careful as it may catch fire if its ignited ,think you'll find its the carb at fault.

Dean

[sideout]

Hi,put a 48 pilot jet in the carb instead of the 45 and give it a good clean out first ,then spay some wd40 or carb cleaner around the intake area but be careful as it may catch fire if its ignited ,think you'll find its the carb at fault.

Dean

Hi Dean,
I'm working on the principle that a standard GP200 engine should work with a Jetex which has standard 200 jets in it. I certainly take your point about the fire risk! (Don't try this at home kids!)
So, I bit the bullet tonight and pulled the top end apart.
I noticed the top of the exhaust box had a streak of oil on it, right in line with the head gasket.

However, when I took the head off there was no sign of oil in the vicinity, or evidence of any burn marks (ok I've only done 20 miles, but I thought something may show.)


Next I'll examine the exhaust, inlet and base gasket, but I bet it's the mag side seal

[sideout]

Hi,put a 48 pilot jet in the carb instead of the 45 and give it a good clean out first ,then spay some wd40 or carb cleaner around the intake area but be careful as it may catch fire if its ignited ,think you'll find its the carb at fault.

Dean

Dean, spot on mate! The 48 pilot sorted it out (after I stripped the top end and remade every joint )

Thanks for the help, I still don't understand why a standard 200 Jetex doesn't work with a standard GP 200 engine. But then it is a Lambretta!

Cheers,

Nigel

[WINTERMODEL150]

Hi,sorry i've not replied sooner but me computers been away,glad its all fixed and i hope you've been clocking up some miles enjoying the sun :fb: