350X Jetting

[cepdave]

Hey everyone,

New to the forum here and really loving it. I have some questions.

I just got an 85 350X. It came with a rebuilt (never started) racing motor. I didn't buy it from the person who built the motor, so I really don't know exactly what it is.

I was told that it has a 410 kit and it has been ported and polished. From looking inside the intake and exhaust ports, I can tell that actually has never been fired. I have no idea what compression it is.

I installed the motor and hooked up the exhaust and the carb which came off a 400ex. It appears to be new.

My first thought when trying to kick it over for the first time was that the piston was hitting the spark plug. Turns out that is not the case, it's just VERY hard to kick over. I have to jump on it with all my weight and sometimes that's not even enough. It backfired once and the end of the kick starter poked a hole through the bottom of my work boot. Ouch, THAT HURT! I did some playing around with the compression cable adjustment and got it to be a little easier to kick over. At this point I'm seriously considering electric start.

I can get it running but can't get it to idle. I have the idle adjustment all the way in but that's still not enough. I took the old jets out of the 350x carb and put them in the 400ex carb that's now on the bike. The pilot jet is now a 42.

Now I can't get the bike started again, probably not because it wont, I just ran out of energy from kicking it all weekend. I'm sure I can get it kicked over again in a few days after I've given my leg and knee some time recover. It hurts like hell today.

I took the carb apart to see if the pilot jet was clogged and ended up cleaning the whole carb. Not that it's really dirty, just thinking that I have no idea how old the gas is in it. I'm planning on putting some new gas in it, as well as a new plug, prior to trying to start it again.

I'm thinking it's at least a 50% possibility that it's a high compression piston. I can get my hands on some racing fuel at Sunoco. I'm also a private pilot so I can also get some 100LL fuel. I would assume it would probably run great on either of these fuels. Thoughts?

When I look at the plug, it seems that it's still quite lean. I haven't had it running for any significant amount of time on the 42 jet yet. I noticed that my needle does have an e-clip in it. Will adjusting the e-clip have any affect on the idle or is this strictly for the main jet? It runs good enough with throttle applied and I figure I can sort out the main jet once I can get it running and starting consistently.

I'm thinking the 42 jet is still too small. Should I bump it up more, and to what size? It has a DG exhaust and I have not yet put the air filter on. I've had the carb off more than on at this point.

I really do enjoy turning my own wrench. I have the tools and knowledge to do it, though I really don't enjoy messing with carbs, just not my thing. I would rather replace a piston than adjust a carb. :mad:

I would love to hear all your input.

Thanks Again!
David

172384

[barnett468]

Hello cepdave



The following are just my opinios, others will vary.


Just to get bike started you can squirt some flammable brake cleaner down carb, however you should at least install the air filter and lid in which case you can squirt some down through the compression release while holding it open, using the long narrow nozzle, providing there is no dirt in it that can get washed down into your engine.



I just got an 85 350X. It came with a rebuilt (never started) racing motor. I didn't buy it from the person who built the motor, so I really don't know exactly what it is.I was told that it has a 410 kit and it has been ported and polished. From looking inside the intake and exhaust ports, I can tell that actually has never been fired. I have no idea what compression it is. it's just VERY hard to kick over. I have to jump on it with all my weight and sometimes that's not even enough. It backfired once and the end of the kick starter poked a hole through the bottom of my work boot. I did some playing around with the compression cable adjustment and got it to be a little easier to kick over.I'm thinking it's at least a 50% possibility that it's a high compression piston.

Others will know better than I however even if it is a flat top piston the extra cc’s can cause it to be difficult to kick over.

I suggest doing a compression test. Use a high quality gauge with a short narrow hose. Turn gas off, drain carb, then test. If compression is above around 175 you will probably need to run some better gas like race gas. Adding methanol or other additives can increase octane ratings but often not by enough and can create other problems.


EXCERPT FROM METHANOL POST

The (R+M)/2 blending octane of methanol is 119. Assuming you will be blending with 93 octane pump gas, at 25% methanol concentration, the octane will be 93*0.75 + 119*0.25 = 99.5.

Although methanol can be blended with gasoline successfully, it has two main drawbacks: (1) of all the alcohols, it is the one which is most corrosive to metal and rubber components in the fuel system, and (2) the resulting gasoline / methanol blend is highly susceptible to phase separation upon moisture absorption. (Phase separation refers to separation of the gasoline into a water-rich alcohol layer and a water-poor hydrocarbon layer.) Another potential problem with methanol is that it is often contaminated with turpentine, which forms a residue during combustion that may cause excessive piston ring wear.

In countries which allow the use of methanol in gasoline, it is usually limited to 5%, and a phase-stabilizing co-solvent is usually employed (e.g. isopropyl alcohol or butyl alcohol).

If you use methanol, make sure it is a grade which does not contain turpentine and also has a very low, water content. Also, don't let it sit in the gas tank too long or corrosion problems may result.

A 10% toluene and 10% isopropanol blend avoids the problems associated with alcohols and the final octane when blended with 93 octane pump gas is in the upper 90's.







I have to jump on it with all my weight and sometimes that's not even enough.

You need to do something about this before you strip the teeth on your kick starter gear or break something else. If this happens you will be sooo unhappy.







I did some playing around with the compression cable adjustment and got it to be a little easier to kick over

A larger volume one may be required.







At this point I'm seriously considering electric start.

This will not correct a detonation problem if the compression is high enough to cause one.







the carb which came off a 400ex. It appears to be new. I can get it running but can't get it to idle. I have the idle adjustment all the way in but that's still not enough. I took the old jets out of the 350x carb and put them in the 400ex carb that's now on the bike. The pilot jet is now a 42. I took the carb apart to see if the pilot jet was clogged and ended up cleaning the whole carb. Not that it's really dirty,

I would make sure the throttle cable has free play so the slide can drop all the way down. Check play between slide and carb body, if it feels like more than around .002” than the carb may be worn out. Set fuel mix screw to stock setting, around 1 ½ turns out from full in. See manual in link below for spec.

Once it runs I would spray flammable brake cleaner around intake boot using the long narrow nozzle. It rpm increases you have an air leak.

Pull plug out and see if it is wet. If so it is flooding.







I have no idea how old the gas is in it. I'm planning on putting some new gas in it

Put some gas in a clear glass, if it is apple juice color or darker it is bad and can make it difficult to start and cause it to run poorly.







a new plug, prior to trying to start it again.

Lay it on the head to check spark. Is it bright blue or pale yellow?







When I look at the plug, it seems that it's still quite lean. I haven't had it running for any significant amount of time on the 42 jet yet.

It typically takes 45 minutes of running time to get reasonable color on a plug if it is rich enough to give color at all.







I noticed that my needle does have an e-clip in it. Will adjusting the e-clip have any affect on the idle

No however if it has a burble/sputter off idle it is rich so drop the needle and try it again. If it has just a flat spot with NO burbling/sputtering than it is lean so go up on needle. If needle is in middle position and going up on it corrects flat spot then either fuel mix screw needs adjusting or pilot jet is too small. If it burbles with it all the way down then either fuel mix screw needs adjusting or pilot jet is too large.







or is this strictly for the main jet?

1/4-3/4 throttle mainly.







It runs good enough with throttle applied and I figure I can sort out the main jet once I can get it running and starting consistently.

Seems reasonable to me.







I'm thinking the 42 jet is still too small. Should I bump it up more, and to what size? It has a DG exhaust and I have not yet put the air filter on.

Put the filter on and lid to air box. Std pilot is 45 for std carb for your bike. This should still be enough for the 400 carb. I would try to start it with no choke and ¼ throttle a few times then look at plug if it doesn’t start, if it is dry it is lean. Then try full choke with ¼ throttle and if it is still doesn’t start and plug is dry you have problems other than your pilot jet, lol.







I can get my hands on some racing fuel at Sunoco.

It won’t make it start easier however as mentioned above, you will most likely need it to eliminate detonation.







I'm also a private pilot so I can also get some 100LL fuel. I would assume it would probably run great on either of these fuels.

Av gas is not ideal for non aviation use, race gas is far better. 100LL has a MON rating of 100 and approximate RON rating of 108 so R+M div by 2 = 104 automotive pump rated octane.

AV gas is not oxygenated, pump gas is.

Av gas is lighter than pump gas so it requires richer jetting than pump gas.







When I look at the plug, it seems that it's still quite lean. I haven't had it running for any significant amount of time on the 42 jet yet.

It typically takes 45 minutes of running time to get reasonable color on a plug if it is rich enough to give color at all.







I'm thinking the 42 jet is still too small. Should I bump it up more, and to what size? It has a DG exhaust and I have not yet put the air filter on.

Put the filter on and lid to air box. Std pilot is 45 for std carb for your bike. This should still be enough for the 400 carb. I would try to start it with no choke and ¼ throttle a few times then look at plug if it doesn’t start, if it is dry it is lean. Then try full choke with ¼ throttle and if it is still doesn’t start and plug is dry you have problems other than your pilot jet, lol.







I really do enjoy turning my own wrench. I have the tools and knowledge to do it, though I really don't enjoy messing with carbs, just not my thing. I would rather replace a piston than adjust a carb.

Well you just might get your wish, we’ll see, let’s hope not.

[cepdave]

Barnett,,,

Thanks for such a greatly detailed response, I couldn't have asked for more. Also a VERY SPECIAL thanks a for warning me bout stripping the kick starter gear. I know I would have screwed this one up had you not given me this advise. I would probably be splitting the case open very soon. So THANKS for saving my motor!!!! :D


I do have a couple questions.

Your response "a larger volume one may be required". Do you mean a larger decompression valve?

BTW,,, even with the spark plug removed it's still difficult to kick over than I would expect. I would say that the spark plug hole is not enough to release all the compression because it pops on the compression stroke.

Can the decompression valve come in contact with the piston if it's not adjusted properly. I don't yet fully understand how the decompression works. My last bike was a two stroke and was so easy to kick.

LOL... thanks for the comment about changing the piston. I would really prefer to ride it this summer before needing to dig into it. I'm more than happy to dig into over the winter as I'm hoping to powder coat the frame and a bunch of other bits as well as ceramic coating the headers. :)

Thanks Again!
D

[keister]

Several of us have 400 big bore kits on our 350Xes. We all have 50 or 52 pilot jets in our stock carbs.

[barnett468]

Hello cepdave





Barnett,,,

Thanks for such a greatly detailed response, I couldn't have asked for more.

You’re very welcome, hope at least some of it benefits you.






Also a VERY SPECIAL thanks a for warning me bout stripping the kick starter gear. I know I would have screwed this one up had you not given me this advise. I would probably be splitting the case open very soon. So THANKS for saving my motor!!!!

No worries, I’ll just send you mt next bar bill and we’ll be even, lol.







Your response "a larger volume one may be required". Do you mean a larger decompression valve?

Yes, if there is enough room on the head it can be done. Probably one off an old 74 501 Maico ought to be big enough, lol.







BTW,,, even with the spark plug removed it's still difficult to kick over than I would expect. I would say that the spark plug hole is not enough to release all the compression because it pops on the compression stroke.

I’m not surprised, a typical 350 4 stroke single is hard enough to kick over so making it a 400…

I saw a 2 stroke 450 kick back and break a racers ankle before.

Our shop built around a 500 cc engine out of a 74 XL350 back in 74 for a desert pro racer the shop sponsored and I couldn’t start it, lol.







Can the decompression valve come in contact with the piston if it's not adjusted properly.

I don’t know the answer to this on your bike with your particular piston. Someone else here should.







I don't yet fully understand how the decompression works.

It’s exactly like a valve and valve seat in an engine cylinder head. When you pull the lever it pushes the valve away from the seat allowing air to flow past it, and just like an engine valve, the bigger it is, the more air that can flow past it for the same amount of lift [distance from the seat].







My last bike was a two stroke and was so easy to kick.

Must have been a 175 cc street bike, lol.







LOL... thanks for the comment about changing the piston.

Someone here should know if it is even possible if it has a dome. Either way, you can get a custom piston made if need be. You might be able to borrow a “bore” scope if you know someone that works at an automotive repair shop, then you can simply look at it and see.







I would really prefer to ride it this summer before needing to dig into it.

Well once you b get off of your crutches you can have at it again, lol.







I'm more than happy to dig into over the winter as I'm hoping to powder coat the frame and a bunch of other bits as well as ceramic coating the headers. :)

That should make it look nice!







Several of us have 400 big bore kits on our 350Xes. We all have 50 or 52 pilot jets in our stock carbs.

Well, there’s at least one answer for ya. If you put in a 50 or 52 it may still need some fine tuning which will depend upon on the cam, your fuel, your elevation, your outdoor temp and your XE400 carb but since you don’t have any jets just yet you can still do the easy tests I gave you if you want.






PS
Hopefully someone will come along with a piston answer for you too.

[cepdave]

Wow,,, I wouldn't have guessed that big, but makes sense to me. I can tell I'm not getting nearly enough gas to start it with the 42's. I'm going to order a bunch of jets today. Thanks!!!!

[cepdave]

I'm hoping to work on it again tonight/tomorrow. What plug and gap should I start with on this setup? Thanks Again!!!

[cobradude]

On the 350x, the decompression cable pulls a lever on the head when you kick it over. This lever turns a rod that runs into the head & slightly holds the exhaust valves open when you kick it.

Barnnet, what are you talking about, using a decompression pin?

[cepdave]

Thanks Cobradude. I actually dug into it last night and can see how it works. Now I just need to adjust it properly.172415

[cobradude]

Welcome! You need a manual if you don't have one. Major props to you for taking it apart and seeing for yourself how it works. manuals can be found here:

http://www.oscarmayer.net/atc/manuals/