Opened up the engine, looky what I found

jaybob · Post by **jaybob** » Mon Apr 06, 2009 10:50 am

What I found was really fat jetting but tell me, it seems that it may not be inappropriate.

Anyway, in getting ready to re-jet my carbs and install my shaved head I tore the top end down last night. I also wanted to verify the bore size and check on any port chamfering etc....

First up the bike ran pretty good before (I hope it does after also) claimed to be on a fairly recent .5mm overbore, and opened up airbox as the only mods. I don't know for sure but it kind of looks like the carbs may have been bored or honed.

Since I am installing the Jemcos I pulled the carb rack to verify my jet sizes. What I found was
25 pilots all the way across
117 mains in the left and right
112 main in the center
I forgot to pull the needles yet
Seems like really big main jets but here is a pic of the plugs (they look pretty good

Also the cylinder tops

Left

right

center

Stock cylinder head

Looks like the jetting is acceptable? It kind of surprised me since all of the specs I have read claims some smaller mains.

Here is the spare head I got and want to try out

I need to jet the carbs for the following mods:
Jemco Pipes
Head skim
Uni Filter pods

What say ye? Go up 1 or two on the pilot? Then run 117's all the way across or should I go even larger on the mains? From the plug read is it too rich? Those mains sizes seem right for a modified 750 LOL!!

Jason

H2RICK · Post by **H2RICK** » Mon Apr 06, 2009 11:11 am

I don't know how many miles are on that new top end but it looks like 5 or 6 thousand at least. If it isn't AT LEAST that many miles, then STOP using the injector oil that's in the bike. There are 'waaaayyyyyy too many non-combustibles in that oil from looking at your pics. Try a full synthetic to stop the crud buildup.
As to jetting: The jets that WERE in it as per your post 117.5 - 112.5 - 117.5 have too small a centre jet. There should be only ONE jet size difference between them, so the centre jet SHOULD have been a 115.
You should probably order: First set= 2 of #122.5 and 1 of #120
Second set= 2 of #125 and you can use 1 of the #122.5 from the First set in the centre cylinder for this set.
Set your needles on the rich side, which means put the clip in the fourth groove from the TOP of the needle.
Then you can start reading plugs. I would put the Second set of jets in first.
You can always put the leaner set in if required.....but you can't weld up a hole in your piston crown if you put the leaner set in first....if ya get my drift.

jaybob · Post by **jaybob** » Mon Apr 06, 2009 12:07 pm

Yeah it's got some miles on it. I tried to find out more details on exactly what was going on with this bike after I bought it. I even talked to 2 previous owners. When I was talking to the guy that did most of the work on the thing he was an older gentleman and was having some difficulty remembering all of the details of what I was asking him.

I have discontinued used of the previous oil. It was told to me that it was some sort of outboard motor oil.

Barry S. · Post by **Barry S.** » Mon Apr 06, 2009 12:43 pm

If you will polish the combustion chambers in the head carbon will not stick as much, make them shine.

Craig380 · Post by **Craig380** » Tue Apr 07, 2009 1:49 am

I'd say that looks pretty good, and some decent 2 stroke oil will help keep it that way.

One tip I can recommend is using the NGK platinum plugs (EVX). You can order them pretty cheap online, and they simply never seem to need cleaning or gapping. Just set the gap to 0.7mm and forget them.

Every little helps, especially if you're running the stock points ignition.

Triplerocky · Post by **Triplerocky** » Tue Apr 07, 2009 4:22 am

those jets seems really huge for a stock 380.... it comes with a #80-80-80 main jet set (round/button/reverse type), O-2 needle jet, 4DH7 jet needle at 2° notch from the top; from the very last 1977 parts list and applicable to the L,M,A,B model. My 380 (really 399 cc.) got #82,5 mains, no other changes, runs very well with clean and light tan plugs.
What carbs are mounted on yours to carry on such BIG mains?

GT Tim · Post by **GT Tim** » Tue Apr 07, 2009 5:34 am

Not to start an oil war...Suzuki CCI. You can't go wrong.

tz375 · Post by **tz375** » Tue Apr 07, 2009 7:09 am

Jason,

Is this a 380 or is this from your 550?

jaybob · Post by **jaybob** » Tue Apr 07, 2009 7:23 am

Rocky

Sorry for the confusion. Stock VM28's This is a 550, but still your same point is a question that is valid and one that I don't know the answer for.

Triplerocky · Post by **Triplerocky** » Tue Apr 07, 2009 7:49 am

Dont' mind.... mea culpa, mea maxima culpa

jaybob · Post by **jaybob** » Tue Apr 07, 2009 10:22 am

After I got my shaved head home last night I was a little concerned with it.

I took it to a very reputable machinist and he had to charge me extra when I picked it up. Turns out that he said the head had a little bit of twist or warp to it, so it took more set up time than he quoted me originally.

Upon my home inspection I am thinking maybe the combustion chamber volumes were not ok because of the difference in the visible ridge around the chamber. It looked like the head was cut deeper in the middle than on the outer chambers.

So I start stressing a little because I am thinking maybe I wasted money and ruined a good part.

The only thing left to do is measure it somehow. I called up my Dad who works on Sprts cars and I ended up CCing the head last night. I was able to use good old Dad's CCing kit. Silly me I forgot to bring the stock head for comparison.

However I am super happy to report that through my imperfect method of measuring the volume (I am sure I lost a drip here or there) All of the combustion chambers measured within .5cc of each other. Right at about 21CC

Tonight I will bolt the modified and the stock head on and take a compression reading for each one. I can't wait to find out the results!!

Post by **oldjapanesebikes** » Tue Apr 07, 2009 1:27 pm

GT Tim wrote:Not to start an oil war...Suzuki CCI. You can't go wrong.

OK - so rather than have a war over oil

how about one over spark plugs ?? Any thoughts out there on resistive versus non-resistive plugs for these older machines ?

Post by **oldjapanesebikes** » Tue Apr 07, 2009 1:32 pm

jaybob wrote: The only thing left to do is measure it somehow. I called up my Dad who works on Sprts cars and I ended up CCing the head last night. I was able to use good old Dad's CCing kit.

I've thought of doing this a couple of times, but never actually got round to it - how exactly did you do the measurement ? Eyedropper ?

GT Tim · Post by **GT Tim** » Tue Apr 07, 2009 1:36 pm

Always used non-resistor NGK's in my 2 stroke Suzukis. One of the beauties of Suzukis w/ CCI oil, when they are set up right, they don't foul plugs.

I don't have any experience w/ resistor or other style plugs in 2 strokes.

jaybob · Post by **jaybob** » Tue Apr 07, 2009 1:54 pm

oldjapanesebikes wrote:
jaybob wrote: I was able to use good old Dad's CCing kit.
I've thought of doing this a couple of times, but never actually got round to it - how exactly did you do the measurement ? Eyedropper ?

We propped the head upside down and level.
Installed a sparkplug in the hole.
Ran a bead of grease around the edge of the chamber
Layed down a piece of glass with a small hole in it over the chamber and sealed it with the grease
Then we used a long graduated cylinder mounted on a stand
We placed the cylinder over the hole in the glass
Filled up the cylinder with about 50cc of liquid and wrote down the starting fluid level
Using a valve on the end of the cylinder we slowly filled up the chamber
When the chamber was full we wrote down the ending fluid level and then subtracted the difference for the volume.
We used dyed alcahol for the fluid since it does not have the surface tension and meniscus that water does.

I should have snapped a pic but forgot. Maybe when I do my stock head I will remember.