1986 XT600 Only Start With Starting Fluid, Backfires
 

Hi guys, I just bought a 1986 XT600. Was only $100 (no title) and it started with a little starting fluid, but backfired like crazy. I checked and double check the valves (verified TDC with wooden dowel) and valves are in spec. I cleaned and replaced gaskets and float needle on carbs (need to set float level). I put new intake boots on as one had a gaping hole.

It will only start with starting fluid (bad I know) and will only run under throttle. It backfires like crazy (angry neighbors) and just sounds horrible.

The Previous owner had tried to repair the exhaust with muffler tape (probably exhaust leak) and the airfilter is shot so I need to order a new one.

I just ordered a new CDI for good measure. Hoping my buddy has an extra exhaust to test. Also just ordered a new battery.

For the air filter. I have the airfilter box, do I need to spend $80 on a uni filter on ebay or can I just buy the filter that wraps around it? https://www.ebay.com/p/Uni-NU-2285ST...55092767&rt=nc


Wondering if anyone has any thoughts. I did notice the ground wire coming from the timing chain area was loose. I just connected it to the engine using a cover bolt. Is that ok?

I'm new to dirt bikes but really want to get this thing running. Any help is much appreciated. Gad to be joining this community. Thanks, Ian in Seattle

it could be so many things, maladjusted valves and an iffy CDI least likely.....


some months ago there was a guy who just like you bought an 86 for cheap, ended up spending 1500$ on it, bike still not running, "discovered" a welded sprocket on the tranny shaft which would require an engine disassembly to sort out and then forever disappeared from the forum... cant blame him!



maybe post some pics to see if it's worth the effort fixing so we can save you form similar fate.



Hope you didnt buy by chance HIS heap of bike ;)

That would certainly suck, but I have high hopes. The carbs hadn't been cleaned on this thing for awhile and I'm sure that dude at least cleaned his carbs, right?

I know the valves are good. I've cleaned many a carb, and feel good about its condition, although I noticed the choke is sticking... so need to have a closer look at that. I'm going to pull the carbs and set the float height anyway. I ran a guitar string through every port and jet, so I know things are flowing.

The more I read, the more I wonder if it's the fact that there is no air filter and the air box is wide open (plus the patch job on the exhaust)... just how the bike came. I have new air filters in the mail. It sounds like these bikes are VERY sensitive to air/fuel mixture ratios being off?

Any tips on an affordable replacement exhaust?

Thanks! Appreciate the optimism!

Alright. So the bike is up and running. I cleaned the carbs again (upjetted main to 130), got new air filters, derusted the tank, changed oil and filter, and added an inline fuel filter.

I finally got it started today. Strangely, it only started when I jumped the (dead) battery off of a good Harley battery I had lying around. Does that make sense? I didn't think the ignition system would benefit from battery power...

Anyway, I got the air/fuel mixture dialed in, but I'm noticing some issues.

First, the bike lacks low end power. It just feels weak. It also seems really hard to kick start and the valves are VERY noisy. I've read up on the decompression valve and had a look at it today. It's not clear to me what people mean when they say .5 mm play in the lever. Do they mean the kick start lever or the lever that adjusts the decompression valve on RH exhaust valve?

I have set the valves twice and last time used a dowel to be sure I was at TDC. Everything seemed right. There was a slight play in the valves as there should have been.

Could the valves need to be redone?

The really bad news is that the engine is leaking oil from the very bottom of the bike. Right at the split in the middle... What should I do with that?

Appreciate any tips!!!

Have you done a compression test? It could be low compression due to worn out piston rings and bore or a problem with the valves. If it is low you might get away with new rings and breaking the glaze in the bore and a valve regrind or if very bad a rebore and piston along with new valves.

0.5mm slack is in the decompresser-lever.


Did you adjust the valves at the right TDC? The right one comes after the intake valves closes, and before the exhaustvalves opens. So inbetween that.

Thanks Jens! I'll have a look at that lever and then double check I set the valves correctly according to your advice! :thumbup1:

Does anyone know the stock pilot jet size for the 86 XT600?

I've read on new models that going up to a 48 is beneficial. Is this a good size for me to order?

This is for the 90's XT600. Would it work in a 1986 with Teikei Carbs?

https://www.cmsnl.com/yamaha-xt500e-...48_43f1434224/

I also found these for a TT600, but they don't have 48 or 50:

https://www.jetsrus.com/a_jet_kit_di...600_TT600.html

Stock pilot for an 86 XT600 is a 46. Going to a 48 will not solve your problems. Did you spray carb cleaner down the pilot jet hole to verfiy no blockages in the carb internal passages? You should get carb cleaner coming out of the main pilot jet hole and the air screw hole in the venturi.

Get it running right with stock settings before you mess with it. What needle clip positions are you running? Should be 4th notch from the top on both needles. What exhaust you running? I have found stock muffler to give best torque in low RPM range

Are you sure the timing chain hasn't jumped a tooth?
With intake and exhaust too free flowing your mixture would have been way too lean for cold starting - sounds like you've got that sorted.
Keep at it - you'll win in the end!

Pics could help understand general condition of the bike...

Hi mate, my 89 XT600 3ew has exactly the same problems you quoted, did you nail down what the problem was or do you still think it had something to do with the battery?