Fuel out of top of carb

[Vespresso]

Guys! After rebuilding my engine, following the clutch side oil seal failed, I'm still unable to get it started. 

The issue seems to be that fuel is not going into the chamber, it's being spat back out of the top of the carb, and not just in small quantities. 

Any ideas??

[vespasco]

Renid us of your set up, crank

Have you fitted an air filter to the top of the stock? carb?

[Vespresso]

Malossi 210, was running a 26mm standard type carb, with 135 main jet, Sip 2 road exhaust, have tried a new 24mm carb with 126 main jet.

Either set up won't start but does occasionally fire, when kicked over, fuel spews out of inlet (with filter removed), also, just noticed fuel running out of carb box??

[pxguru]

The obvious answer is some carb or float needle leak but could also be a CDI issue, or even the piston upside down. So many choices

[sneillyboy]

CDI Issue ?? Unsure what u mean ?

[vespasco]

Start with basics.

Check you are getting a spark.
Set your idle mix screw to 2.5 turns out.
Check your timing if it's moved or or been refitted.

Have you fitted new gaskets beteeen the carb air box and cases? And carb to air box?

Correctly torqued down carb, evenly.

If all that is fine, do check your timing properly.

The CDi could be misbehaving, not producing enough spark at the right time. If you happen to have a spare swap it over to check it.

There's going to be some spit back.
But it does sound excessive

[Vespresso]

Thanks for your feed back.
I am getting a good regular spark.
Idle mix screw is set to 2.5 turns out.
Timing has been reset.
New gaskets have been fitted between carb box and carb
New CDi fitted & producing enough spark at the right time. Piston is on correctly.

There Is loads of spit back, so much that petrol is ending up on back light and seat?

[henri]

crankcase has to be getting pressurised for that much fuel to get spitback . 2 causes come to mind , reversed piston , weve all done it 1 time at least .or trapped/damaged rings ,easily done on assembly ,or if ring gaps not checked before assembly . H

[Vespresso]

Although the crank has been removed to change the oil seal, the piston was not removed from the con-rod, so the piston cannot be on the wrong way.

The barrel slips over the piston & rings very easily, in my mind, a bit too easily, as from memory, in the old days with a stock top end, we had to use a ring compressor, but with this 210 Malossi, they slip on like, well, very easy, is that normal with this top end?

Good point on the crankcase being pressurized though H, that does seam likely??

[vespasco]

Is it a stock crank?
With stock timing?
Any other porting?
Are the cases matched to the cylinder?



You can measure the gap on the piston rings

[Vespresso]

I'm not sure if it's a stock crank, how can I tell, and what difference would that make?

The casing do look like that are matched, but not 100% sure as I don't really know what to look for, but the timing is set to 18 degrees BTDC, as per Malossi website.

[henri]

if somebodys been "cutting" the crank ,to increase the inlet time there will be evidence/marks on the crank web at the ends of it .the part that when looking down inlet can be seen opening an closing the inlet. if done too much/wrong the inlet will still be open when pistons descending an trying to compress the mixture in the crankcase. as crank was in before an runnin ok ,dont think this is the case .
wether you need a ring compressor or not is usually down to the barrels ,they should have a taper/angle machined in the bottom of the spigot so rings are compressed by barrel itself.if re-bored this is often not re-machined makin piston installation harder .you say it went in easy ,to easy to your mind , sometimes they do ,but not often . worn or trapped rings allows the gases past pressurising the cases .means fuel spat back out the carb an often a blown seal ,clutch or fly or even both .rings should move freely in the grooves in piston ,an when popped into the bore the end gap must be .25mm or more .the maximum is 2mm but i'd replace any over 1mm . H

[cakey]

Have you sorted your fuel problem out as I have a similar set up with a similar problem. Mine starts and ticks over fine but when I rev up fuel blows out and builds up before running down the crank case any help would be appreciated