GPR Camp: Replica Racers

Looks like the 'saerch' functionality is pooched right now (getting a 500 response code) so try this link -
viewtopic.php?f=17&t=326

These leak down testers are a MUST HAVE for any serious two stroke engine mechanic. In my experience air leaks are the number 2 cause of engine failures (right behind badly adjusted carbs....) and this is an invaluable addition to the tool box.

Rj_666 wrote: ↑

Mon Sep 28, 2020 9:03 pm

You might care to search the forums for 'leak down tester', and use something of that nature rather than checking with carb cleaner / whatever...

A leakdown test won't tell you if there is a vacuum leak at the intake manifold connections.

Using Carb Cleaner/whatever will tell you immediately.

Also run the risk of fire... that said, I check my bike with the manifold on, and the 'plug' inserted in the rubber boot ALL the time.....

I guess YMMV.

A little annoying a new malossi viton manifold'boot' costs 48 euros where as the kit only costs 66 to 76 euros. bit of a rip off .. Maxiscoot offered me a top performance replacement manifold for 18 euors. when I said the base looked different they said just modify it.. not sure what that means or to what extent.. so may end up getting a new intake manifold kit.

Rj_666 wrote: ↑

Tue Sep 29, 2020 6:35 pm

Also run the risk of fire... that said, I check my bike with the manifold on, and the 'plug' inserted in the rubber boot ALL the time.....

I guess YMMV.

In that case yes, but with the carb in place - no.

Spraying around the manifold with Carb Cleaner is not dangerous or difficult to do, and tells you immediately if you have a leak. You could get a good seal using a plug with a leakdown test, but when installing the carb could have a leak between the carb and manifold and not know it.

Hi guys, just a quick one here.. Bike was running fine ticking over. About an hour later it couldnt start even when bumping it.

I thought of the carb manifold so have ordered a new one but noticed some petrol at the base of the cylinder head. I went to recheck the cylinder head nuts and seemed loose as was using a torque wrench but dont know how I over tightened it I snapped the bolt.

In stripping down the head I noticed some score marks on the cylinder.. doesnt feel rough to the touch but does it need replacing??? .. as far as i can see the cylinder is in great shape




Cheers

Can you post photo of piston crown and underside of that piston? Is there any burnt oil underside or is it completely clear?

Sure.. here you go

It's clear that this piston is overheated... There should be absolutely no burned oil underside. And grey center of piston crown is another sign. Now, what is the reason for this is another question, air leak, lean jetting.... I'm not sure, but thats spots on the piston could even mean presence of detonation? What does spark plug look like?

Cool thanks man.

The temp sensor hadnt been working .. found out it was a frayed wire.. so ordered a new one . such a shame!

carb setting same as before , jets the same etc.

Water pump looked ok.. except the hose down from the radiator to the pump was empty but as always the expansion chamber full.. I assume that this is the norm ?? if not then heres the problem.

air/fuel mixture wound in quite some so no excessive air there.. could be the air leak making it lean? and hence the setting i have.

spark plug looks the same as the side of the crown.. quite carbony. note on the crown the lighter part is where i held it in the middle.

if the cause found then can i still use the piston and cylinder or have to order a new piston or both?

thanks again.. much appreciated1