PE175 jetting

[pmc57]

I'm trying to get a Suzuki PE175T running as I think it should. It's been rebuilt with new main bearings and seals, this was mainly because the main bearings were badly worn and rattling quite badly so they needed replacing anyway.
Before the rebuild she didn't really didn't have a crisp mid range throttle response and now after the rebuild performance hasn't changed too much, except now there's no main bearing rattling as you would expect. The top end was fine and all within spec.
I'd expect a response something like with a quick rap of the throttle in the right gear and rev range in 2nd or 3rd it  would produce a nice front wheel lift or a power tail slide as and when required. This engine just doesn't do it. Even at full throttle it just doesn't seem to want to rev right out quickly as you would expect from a so called de-tuned RM. In low rev and high torque required situations like hill climbs and 1st gear work it seems to perform as required, so I'm thinking it may be the jetting of the little beast that's the main issue. As per the book all is very close to spec for the 34mm carby fitted. Main jet #250, Needle jet R-3, Needle 6DP17 (middle clip position), pilot #2.5. slide cut-away #2.0.
My thinking she may be running a bit on the rich side through the mid and top end rev ranges. The plug that's in it is a B8EGV, standard spec calls for a B10EGV, this sort of tells me that it may have had a past history of running rich so a hotter B8... plug was used to stop plug fouling perhaps, (I've only had this bike for a few months) or the other thing that i think is the prob is the timing could be a bit retarded eventhough the sator plate alignment is where it should be.
Should I be looking at leaning her off a bit by dropping the needle a notch or two as well as using possibly a #230 main jet? Also what's the best way to do a physical check with the timing?
Only thing that's not standard is she has a DG head fitted and had a port clean-up but not altered. 
Any comments or assistance to get this bike performing better would be appreciated.

[LWC82PE]

i recommend you join up here and i will get you on the list ASAP
http://groups.yahoo.com/group/PEmotorcycles/
the 175 T had sketchy jetting from standard and many people have found them difficult to get right. The fix back in the day was to stick on a Dellorto from Geoff Udy Suzuki.

there are a few other guys on this forum who have jetting issues with the 175 T and would be able to share info.

from std the fuel recommended was 95 octane. the higher compression DG head you should be using a higher octane fuel. at least 98 but i would say you may need to mix in octane booster or use Avgas. be very carefull with this head because if everthing else is not set up and tuned to suit you will damage the motor and is why you see many DG heads with signs of detonation and overheating.

the jetting specs in the PE books are for use with 20 to 1 oil mix. i dont recommened anything other than this in a PE. if your using more or less oil then jetting needs to be adjusted to suit and you cant go buy the book. also dont go by the cylmer manual. the jetting specs in there are for USA models and are quite often different to australian models. contact me if you wish to know the Australian jetting or if you get onto the PE forum you will find them on there.

i would recommend checking the timing with the head off and using a dial guage or degree wheel. dont trust the timing marks on the stator plate. once set up i would check it with a timing light. Also i have a feeling that the timing may vary depending on country as well, although im not 100% sure. different countries also used different thickness head gaskets on some PEs.

i would also try it out with a std head first aswell. once you can get it right with that then look into tuning with the DG one

[pmc57]

Thanks for the helpful information LWC.... I am currently running at 20:1 with 98 octane unleaded, although I might put a std head on and see if it makes much difference.
You mention checking the timing with a dial and protractor wheel, but how do you know when firing is with the CDI unless you run with a timing light. Does the mark on the stator plate align with another mark to confirm correct BTDC?

[LWC82PE]

yes there will be a mark on the case near one of the mounting slots. you line the mark on the stator plate with this mark on the case, which is the center line of one mounting hole. you then put the flywheel back on. there should be another mark on the case and marks on the flywheel. mark the centre line on the flywheel with white paint/texta and then start motor and hold timing light at the mark on the case and flywheel. you kind of need a tacho as well so you rev it to the specified amount and see if its correct. you can get multi meters and special intruments to measure revs that have a lead that clips onto the spark plug lead to read the engines revs. if its a bit out you then remove flywheel, loosen stator screws and then move the stator plate acordingly, refit flywheel and recheck. and if its not reving/advancing correctly, the the CDI is probably faulty. they are a basic unit inside and Betta bikes in Adelaide can repair them pretty easily.

[pmc57]

Good stuff LWC... I was just talking with a friend today and said to him it wouldn't surprise me if the CDI was faulty. Anyway I'll try the std head and try my best with the timing, if those two fail, it may well be the CDI.
Anyway it gives me somewhere to start.

[pmc57]

A bit of an update. Checked the timing with a timing light tonight, it seemed to be slightly retarded so I've adjusted it back to where I think it should be. As said I've only done it tonight so I haven't had a chance to take it for a ride yet.
Also one other abnomality I did pick up. The needle jet that was in the carby was a 348 Series R-3. As far as I know, the standard Series needle jets in most Mikuni's to suit PE's and RM's should be a 159 Series. The 348 series jet has a shorter half round cap section that sits exposed up in the carby throat through which the needle goes. Again I haven't taken it for a ride yet (too late tonight) but I have a feeling this might be the problem. My thoughts are it would inhibit or alter the normal ventury effect which may be causing my mid range sluggishness.
Any thoughts.

[LWC82PE]

if you think its too rich in the mid throttle maybe take a bit off the slide cut away. this was a fix done to many PE's especially the 400's where it is recommented to grind off 1mm of the slide. some of my carbies have had this doen to them, but remember once its gone you cant put it back on! maybe get another carby slide to modifiy. PE 34/36mm mikunis can be easily found on ebay.

also if you think its running too rich overall, take out the choke plunger. its becomming all the more common now that the sealing rubber on the end of the brass choke plunger are becomming, hard and perished as well as having a groove worn in where they have been sealing and effectivly dont seal off/only partly seal the choke, so your getting a richer mixure all the time and its like you have the choke partly on the whole time. i have experienced this a lot on Amal MK2 carbies fitted to britsih bikes which are basically a Mikuni round slide copy, and ive started to see it more now on 25-30 yr old mikunis. tuning difficulties can be traced to this tiny rubber.

it was only this morning that i fixed this on a set of Amals i rebuilt. STD procedure is to check out these choke rubbers, and sure enough they were hard and perished so i used a hole punch and punched out 2 new rubbers out of some neoprene rubber sheet. you gotta use something thats obviously fuel resistant. you could also use some polyurethane or viton sheet or punch a piece out of some fuel line. sometimes you can also buy the choke plungers with the rubber as spare parts but cutting your own rubber seal out is cheap.

this is something i know plenty of people dont think to check. i do know that when you do fit new rubbers it makes a noticeable difference.

[pmc57]

You know LWC... you and I must be on the same wave length, I was checking the choke plunger rubber the night before last. It seemed a bit deformed but there was still plenty of spring pressure on it. I might still replace the rubber though, just to make sure. Does the old rubber just pry out with a very small screw driver or knife blade?
I'll be giving the bike a run this afternoon as soon as I get home from work to see if the change of Needle Jet does anything.
I'll keep all informed.

[LWC82PE]

yes. i use a pin or tiny jewlers flat blade screw driver. good luck.

[pmc57]

I think I've got it as good as it's going to be. Response is much better, not sure if it's the correct needle jet or the timing, probably a combination of both I'd say.
I'll still do the choke rubber though.
Thanks for your help.
pmc57