PE175 Jetting

[Stewy138]

I have a PE175C - 78 model with the original 32 mm carb, which has a (stock) 190 main jet.

Have made porting mods - lifted exhaust by 1mm, dropped inlet by 4mm and cleaned up transfers etc.  The plug runs a light tan, and the engine seems to have symptoms of too lean a mixture in general.  Not much smoke from the exhaust and when i get into the top end on a hard ride the engine chokes (severe hesitation) and I need to roll back the throttle to get on the herbs again.  Compared to Mainlines PE175T there is bugger all mid range but the top end is strong.

Anyway so I have dropped the needle circlip by one rung and am thinking I need a larger main jet - but what to choose.  Just wondering if anyone has jetted a PE175C and what the outcome was.

Thanks,
Andrew

[lukeb1961]

standard was #190 with options of #200, #210 and #220
You can still get these easily. Dropping the needle circlip helped a bit? I would try a #200 main.
You are running a BR9EV plug, yes?

[Stewy138]

Luke, thanks mate.  I did try dropping the circlip a while back and only got up to the mid range in the back yard. Didnt seem to make much difference except for the amount of smoke.  The plug is a B10EG.

[LWC82PE]

correct original PE plug is a 'EGV' or better still use a modern 'EIX' (iridium)

[Lozza]

When I timed Luke's PE cylinder I can remember port timing was fairly good. I feel thw 4mm off the inlet might be contributing to your jetting drama's. I would say a 9 plug would be more in line with a PE's intended use.

[pmc57]

I agree with Lozza on the plug heat range, the 10 may be a bit too cold and causing intermittent fouling. I'd also think that it may be not breathing all that well, you mentioned you opened up the porting, although 4mm lower on the inlet does seem a bit extream but it may want more exhaust flow so I'd be looking at the pipe as well.
From memory the PE pipes had a restrictor mid section in the standard pipe, you may have to look at removing that to let it flow better. There is some information on this mod in one of the manuals for PE's altough I'm not sure which one.
Check all the jetting right from the pilot through to the main and the slide cut-away, but a larger main may be needed particually if you open up the pipe and get it reving higher.
 

[Stewy138]

The pipe I am running is from an RM125C with the front section (40-50mm or so) chopped off and replaced with the larger PE section so that it matches the barrel.  The muffler is a straight through home made job. 

The inlet poirt thing was as per the recommended mods for a PE175N in the publication Two stroke performance tuning by Graham Bell, and I think was actually only 3mm.  Graham says that the stock inlet duration is very conservative to give a wide power band, but lacking in power compared to 'other 175s'.  Still at 3mm lower the timing is pretty conservative compared to a ported RM125C.

I lapped 0.2mm off the head gasket to give a little more compression.

Thanks for the info about the plug - have found it difficult to get exactly the one I wanted (was looking for an N57G equivalent).