Honda XL500R problems after starting

[Basic_]

I'd figure I just open a new topic as my other one concerns another subject...

So I recently bought this 1984 Honda XL500R from a friend. He had left it in a garage for 5 years with half a tank of gasoline.

So, I soon discovered very much rust in the tank and created a temporary tank out of a soda bottle. The carburetor had some rotten rubber parts, so I renewed it with a revision kit.

It starts well, but after a short while (1 minute), it's troublesome to keep running and not long after, it just quits with a sort of an air pluf sound. Then it won't start until it's cold again.

I also renewed the spark plug.

Do you guys think this is an engine problem or an electrical?

It has not got that much compression. So an engine overhaul has to happen anyway, but I'd like to know what it is.

[Muzz67]

Sounds like as soon as the carb bowl empties , it stalls? Is there a hole in the bottle to allow air in? 

[Basic_]

Hmm.. I will try that one. I had an overflowing carb before and therefore closed the hole in the bottle. But the problem was the carb float.

Tomorrow I'll have time to take a look.

[sina27]

Like Muzz mentioned, be sure to make an hole on top of the soda bottle. When the motor is on and fuel starts flowing from the bottle, its going to create negative pressure inside the bottle which ultimately disallows fuel flow. 

This is why fuel tank caps have air breather hoses to constantly keep the fuel reservoir at atmospheric pressure.

[Basic_]

I closed it because it kept draining when the float was not working properly. It kept leaking even though the the botlle had no hole in it. But now I'll open it again.

[Basic_]

In addition to this post:

 

 

What would be the ideal carburetor for this bike? I've read posts about a Mikuni flatslide in 38mm or 36mm? 

I don't want to have a powerfilter as those things are a hell for finding the proper jet adjustment. Or am I wrong?

[sina27]

Sudco can probably help you out if you want a Mikuni. My XL250 is equipped with a spigot type VM32. Sudco has jet specs for you ready to go. I don't see anything in their user manual about suggestions for the XL500, but if you give them a call or email they

will probably have some good suggestions.

 

Here is where I found jetting specs for my Mikuni Transplant:

https://thexscafedotcom.files.wordpress.com/2012/05/xs650-mikuni-vm-carbs.pdf

 

Dave from xlintperformance.com sent me the VM32, prejetted for my XL250. He also gave me the pod filter and correct throttle cable necessary to install the Mikuni, all for a reasonable price. Even though Xl500's aren't his specialty, it would't hurt to shoot him an email.

 

Please let me know if you get any responses, as I am also interested in adapting a Mikuni for my 1980 XL500s. 

[Muzz67]

An XR500 carb makes a huge difference to an XL. 2mm larger.. An XR flywheel/rotor also is a vast improvement too,, although

for some reason, not all rotors run all the lights sometimes. Dont know why.

[Basic_]

Thanks for the answers.

Special thanks to the ones that suggested the hole in the tank! It worked.

Also noticed some rattling from the cilinder, but maybe it's normal.

The engine leaks and has little compression, so I think an overhaul is no excessive luxury.

Uploaded a video of it:

https://youtu.be/wvGEpCU1s0k

[Basic_]

Standard carburetor for the xl500r is 34mm? So the xr500 carb is 36mm?

An aftermarket is probably easier to find than a xr500... And that one probably also needs new parts

[sina27]

How do you know the engine has low compression? If you think it has low compression because you tested it using a compression gauge, remember that the read could be a false negative because these bikes are equipped with decompression levers.

 

The rattling could be a couple different issues:

-If this motor has a "front balancer", you probably need to tighten it. I had to do it on my XL500s. You have to take the right crankcase cover off, and loosen a couple bolts on the balancer assembly so the chain tightens. Its not hard to do if you have a manual to follow.

-Adjust the cam chain via the cam chain tensioner bolt

-I doubt the sound is from improper valve clearance, but adjust the clearance anyways. 

 

The oil looks like it seeping heavily from the exhaust rocker arm shaft. This is very common, and I just fixed this issue on my XL500s. You need to remove the cylinder head cover, and then remove the dowel pins which secure in the rocker arm shafts. Removing the dowel pins is a pain in the ass. I did this by heating up the aluminum around the dowel pin with a blow torch to allow the aluminum to expand, then pulling out the pins using large vice pliers (be sure to not damage the head cover surface). Once the pins are out, you can remove the rocker arm shafts and rocker arms. These shafts have O-Rings, which is what you need to replace. Find a place that sells high temp O-Rings (usually colored green), and re-install. Be sure to use new dowel pins when installing the rocker arms back in, and be sure to place the wave washers back where they were so the rocker arms will seat correctly. 

While the head cover is off, this is a good time to inspect the rocker arms and cam shaft/cam journals for wear. Make sure valve timing is correct too. If the arms or cam look beat up, you can get the rocker arms hard-welded back to stock specifications through Megacycle Cams. Same thing goes for the camshaft. I ended up buying a "new" camshaft from Amazon for 60 dollars (a gamble, but so far its working great). 

When reinstalling the head cover make sure the surface is smooth, and apply a thin coat of hi temp sealant (I used Hondabond HT which is working great, but many people suggest ThreeBond). 

 

I cant stress enough how important it is to all these things properly the first time around, because taking the head cover back off after realizing you made a mistake is a pain in the ass if your bike is anything like my XL500s. There is little clearance between the head cover and bike frame, so I had to loosen and remove some of the engine mounting bolts to lower the engine to allow enough clearance to remove the head cover. Looks like you will have to do the same

 

Also, anyone know what kind of exhaust that is? Looks and sounds cool, maybe I can put something like that onto my 1980 Xl500s

Edited October 23, 2015 by sina27

[Basic_]

Thanks for the detailed sum up. First of all, the exhaust is a German brand: http://www.bsm-exhausts.de/index.php?page=./main/series_overzicht.php

I find the compression low, because I'm not using the decompression lever. I have a lever, some have the decompression cable attached to the kickstart I saw in videos.

Without the decompression lever, it should be a heavy job to kick it, or not? It is not so heavy, but I don't have much reference.

The rest of your recommendations I will try to execute during winter ?

[Muzz67]

your bike still appears to have the auto de-comp cable running from the kicker to the head? does it still operate?

  Although even with that working correctly, it should still occasionally be very hard to kick if you get out of sequence when pushing it over then kicking hard.

[Basic_]

This is the exhaust rocker cam shaft leak?

[Basic_]

Indeed, there is a cable from the kicker to the head. I'll have to check it... Don't know how, but the Haynes should provide some guidance.

[sina27]

This is the exhaust rocker cam shaft leak? 📎ImageUploadedByThumper Talk1445631424.458368.jpg

 Yes. You see the circular port with the line through it? There is oil all around it, so that is where the leak is most likely coming form. That circular shaft has an O-Ring in it. In order to get the shaft out is what I was explaining to you earlier (can only be done by removing the cover and removing the dowel pins).

The leak seems to also be coming from the contact surface between the head cover and head. 

Either way you will have to pull the cover off, and thats why I recommended doing the top end inspection all at once, while you fix the leak. 

 

It seems like the decompression lever is still connected, thus giving you a false read on your actual compression. When you kick the bike over, the decompression lever acts to pull on the exhaust rocker arm in order to make kicking the bike over easier. You can try disconnecting this entire cable system temporarily just in order to do a compression test. 

Edited October 26, 2015 by sina27

[Basic_]

How are the covers for the index mark and crank called? I want new ones ?

[Basic_]

Never mind, already found the part number

[Basic_]

Tonight I went out and try to adjust the valves to the Haynes specs. Inlet valves: 0,05mm and outlet valves: 0,10mm. 

What a clinical procedure that is. With simple feel gauges it is very hard to easily check the opening. Now it won't start, so I probably did it wrong. The normal kicking procedure doesn't work and there seems to be there's a wrong point where the engine gets a spark.

[Muzz67]

did you check clearances with piston at TDC ( 't'mark showing in the inspection hole,) and all valves loose at TDC?

    there are two TDC's , one at 'firing'(all valves closed with loose tappets.) and another at top of exhaust stroke, where the exhaust valves are open.

  If valves arent loose at that TDC, rotate one complete revolution and check all valves loose.

    Then check clearances.