350x engine tuning help needed.

[p26575r16]

A few years ago I rebuilt my '86 350x. At that time I scored a good deal on a 12.5:1 wiseco piston and freshly bored cylinder assembly. I reused the stock cam which was in great shape, and had the head rebuilt with heavier valve springs and new valves. It also has a cobra exhaust system on it (not a fan of that.....) I have alway's run 110 octane vp fuel in it and it's just never felt right to me. I rejetted it a few times and I just could not find the right combination. It also alway's made a wierd sound like an exhaust leak at the header, but it was not leaking. I only ran it 3 or 4 day's since the rebuild because of this. I assumed it was a blown head gasket and I just parked it because we had a new baby and I have another atv to ride. Which brings us to today, two years after the last time it ran. I am planning a trip to the dunes next month and I decided to get this thing going again. I pulled the atc into the garage and yanked the engine out. I was suprised to find the head gasket was not leaking, and the header looks like it was not leaking either. I next suspected the valves were hitting the piston, which also did not happen. What I did find is a lot of carbon build up on the piston and head. I also noticed some whitish trails around the valves. I checked the valves and they are not leaking. The amount of carbon build up is concerning me, simply because the engine probably only has 20 hours on it since the rebuild. I have no idea of what the white trails are.

So, I guess my question is do I run the 12.5:1 setup, or go back to the stock piston and sleeve, or any other suggestions? Thank you

The picture shows one of the trails, not a great picture, but the best I could take in the garage.

[Liquid-Darkness]

As long as everything is put togeather right and you jet up your main to like 175 or higher, there should not be a problem. Just keep running that 110.

[barnett468]

hello

you have some sort of significant prob, that piston looks like it has a ton of miles. might be oil or too rich or both. the rings might not have seated.

did you ise synthetic oil for the break in?

exactly what color is the plug?

is the plug dry and black or moist goey and black?

does the cylinder still have cross hash marks from the previous hone?

do you know what the piston to cyl clearance is?

what do you mean it never felt right? we can't help you unless we have detailed symptoms like it burbled/sputtered upon acceleration or had a hesitation but no butble etc.?


i might hone it again and install new rings.

[barnett468]

If your carb and exhaust are also stock, I might start with around a 150 main jet with 12:1, VP fuel and 5000 ft. elevation. The stock main is a 138.


What is your exhaust pipe type, carb and main jet size?

[RIDE-RED 250r]

Sounds to me like you are a bit lean.

If a gray/white sparkplug indicates a lean condition, I would surmise that white in the combustion chamber would indicate the same... I could be wrong though,it is a 4-stroke after all!

Also, check the color of deposits in the header right at the head.

I think you just need to richen your jetting specs.

I have found that with just a full exhaust and air filter, most 350x's like at least 1 size richer pilot, and main jet. They will pop and snap like the devil on deccel and get white inside the header

[DohcBikes]

I'm curious as to why you installed HD valve springs with a stock cam. If it "never felt right" I'm also curious as to why you kept running a new engine that way

Since you are not confident in the last rebuild, everything needs to be disassembled, measured and inspected again.

[barnett468]

A few years ago I rebuilt my '86 350x. At that time I scored a good deal on a 12.5:1 wiseco piston and freshly bored cylinder assembly. I reused the stock cam It also has a cobra exhaust system on it (not a fan of that.....) I have alway's run 110 octane vp fuel in it and it's just never felt right to me. I rejetted it a few times and I just could not find the right combination.

It also alway's made a wierd sound like an exhaust leak at the header, but it was not leaking. I only ran it 3 or 4 day's since the rebuild because of this. I assumed it was a blown head gasket...

the head gasket was not leaking, and the header looks like it was not leaking either. I next suspected the valves were hitting the piston, which also did not happen.

So, I guess my question is do I run the 12.5:1 setup, or go back to the stock piston and sleeve, or any other suggestions?

Ok:

Was it making this ticking sound at idle or only when accelerating?

if it was only when accelerating then it is most likely detonation from not having enough octane. it is not ideal to run more than around 10.5:1 compression with a stock cam. some people here have claimed to run 12.0:1 and run on around 89 octane. well the only possible ways they can do this is if they either have around 10 degrees of total ignition timing and run it when it is 50 degrees below 0 outside or they are using E85 gas, or their piston rings are leaking badly which reduces their compression.

imo you might be best served by either running your std set up or installing a fairly big cam from web or megacycle which will lower your compression at bit. running a big cam will reduce bottom end power but increase upper mid and top end power, so simply change the gearing to regain your bottom end performance.





why do you not like your pipe other than it might be "bleepin" loud?

[p26575r16]

Sorry, the site was down for me all day yesterday. It's a 12.5:1 wiseco piston, .20 overbore, stock carb, cant remember what jet I ended up with. Cobra exhaust system, uni filter. I went with heavier springs because I originally planned on going with a bigger cam, but ended up running out of money. The noise seemed to go away in the mid to upper rpm range, but it may have just been "quieted" by the exhaust. The issue I had with the way it ran is it just did not seem to make the power it should have. Felt slightly less powerfull than a stock 400ex to me when going up the dunes. Basically it felt like no improvement over the wore out stock 8:1 setup that was in it previously. The plug was black, but the more I look at it I am wandering if the rings just never seated. There is no way it was too rich, and the black on the plug looks more like blowby black than rich black. The cylinder still looks great. I am going to order a new set of rings for it and do a light hone on the cylinder.

Next question. What are your thoughts on a lightened flywheel? I had a spare flywheel lightened, but never put it on. Should I install it?

Last one. Cam? I was dead set on a powroll cam, but it seems like that company may be done. I can get a webcam still, but is there any other options out there? Thank you again.

[p26575r16]

Oh, I don't like the Cobra because it's way loud. Even with fresh packing in it. I may end up switching that out later, we will see.

[DohcBikes]

OK, thanks for the reply on the OEM cam with HD valve springs. High performance cams are built with high performance springs in mind, OEM with OEM in mind. Heavier springs have a tendency to wear out cams quicker, resulting in loss of performance. On new rebuilds oil with high levels of ZDDP have been shown to prevent wear better than those without.

Have you considered that your valve guides and/or seals may be worn? This is an often overlooked area when dealing with performance loss and oil consumption.

[barnett468]

The issue I had with the way it ran is it just did not seem to make the power it should have. Basically it felt like no improvement over the wore out stock 8:1 setup that was in it previously.

Well, if it was burning oil then your rings were leaking which means it did not have the 12:1 compression it should have. If you had taken a compression test prior to disassembling it, you might know a lot more about the rings etc..

The plug was black, but the more I look at it I am wandering if the rings just never seated.

If the crust on the piston was from being too rich the bike likely never would have run since it occurred in a few hours.

There is no way it was too rich…

How do you know that for certain?

What are your thoughts on a lightened flywheel? I had a spare flywheel lightened, but never put it on. Should I install it?

It is quick, easy and free so go ahead and try it however it will reduce bottom end power a bit and might stall easier when braking while in gear.

Last one. Cam? I was dead set on a powroll cam, but it seems like that company may be done. I can get a webcam still, but is there any other options out there? Thank you again.

Yes, Megacycle Cams. I might run the 162-30 with your high compression. I think the 162-40 is too big for recreational riding. You might need to change your gearing a little to suit your type of riding.

http://www.megacyclecams.com/catalog/Page27.pdf

[barnett468]

ROCKER ARMS - You need to run new or refurbished rocker arms on a new cam. Ask the cam mfg's if they recommend hard welded rockers for the particular cam you want.


CYLINDER CLEANING AFTER BORING – I would brake cleaner it then put a rubber mat in the sink, fill it half full of warm water with lots of liquid dish soap like Dawn. or something with citrus in it like Lemon Joy etc.. then clean it with a brush, rinse thoroughly, spray with WD40, wipe with white paper towel. If the towel looks dirty, clean it some more. The WD will look yellow, not to worry.


OK, now for ASSEMBLY AND BREAK IN...I’m getting ready to duck.

I would NOT use synthetic oil for break in. I would use std non synthetic motorcycle oil. Valvoline is available at most auto stores. Joe Gibbs break in oil is good but needs to be changed quickly. Both have high levels of ZDDP that DohcBikes mentioned.

I use a thin coat of the engine oil, others do something different. If the engine is going to sit for a few weeks or more before start up I use engine or ring assembly oil.

I typically let them idle high for 3, 15 minute cycles with a fan blowing on them before riding.

If you want further break in suggestions just ask, I’m sure you’ll get lots of good info.

[RIDE-RED 250r]

So, does the problem of poor running seem the worst at low speed/RPM? Almost like the engine is working against itself?

[p26575r16]

Update: I think I figured it out...
The whitish trails had to be from the 110 vp fuel that I was running. Must have leaked down into the cylinder when I let it sit. There was a trail in the intake and the staining was also in the carb. After removing the piston I found that the buildup was not quite as bad as I originally thought. I believe it was from the piston rings not seating properly. The cylinder had a wierd glaze on it, I believe it was from the rings not seating and allowing oil by them. Lastly, the noise. believe it or not, I think the head gasket was the culprit. I was in a hurry when I put my newly rebuilt head on it the last time, and I did not compare the new headgasket to the old one. I also bought a cheap one. Both stupid mistakes. Anyway I think the valves were actually hitting the heagasket a little causing the noise. I remember now that as the day went on the noise got quieter, and after looking at the headgasket closely I can see some distortion around the valve area.

The fix:
I ordered a new set of rings from wiseco, and a head gasket kit from cometic. I then gave the cylinder a light hone and cleaned the crap out of it. Next I fit the rings to the cylinder and installed all said items. Then I adjusted the valves (having the engine out made that super easy). Reassembled the trike and put some fresh 110 in it. Fired up on the second kick and purrs like a kitten, no bad noises! I ran it for about 5 minutes tonight in my garage. I live in a condo complex (not for much longer thankfully), so I did not want to run it too long here. I'll take it out this weekend to do a shake down run. Then next friday its off to Sand Mountain NV for a much needed ride weekend.

[p26575r16]

If all works out good at sand mountain, I'll be ordering a cam and rocker harden for it.