First Bike - No Idea What's Going on

5twins

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Yes, that looks like a later tank, '78 or '79 since it has two petcocks. I see it has the vacuum petcocks as well. They need a vacuum line hooked up to them in order to flow fuel in the "ON" and "RES" positions. Normally, it runs from a small nipple on the back side of the petcock to another on the intake manifold. You can see them here, they are the orange hoses .....

AEGDnIi.jpg


qAwJKz2.jpg


Without vacuum lines, the petcocks will only flow fuel in the Prime ("PRI") position (lever pointing straight back). Also be aware that the Prime position pulls it's fuel from the Reserve stand pipe, so if you run out of gas, you will be really out with no back-up.
 

Silviculturalist

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Yes, that looks like a later tank, '78 or '79 since it has two petcocks. I see it has the vacuum petcocks as well. They need a vacuum line hooked up to them in order to flow fuel in the "ON" and "RES" positions. Normally, it runs from a small nipple on the back side of the petcock to another on the intake manifold. You can see them here, they are the orange hoses .....

AEGDnIi.jpg


qAwJKz2.jpg


Without vacuum lines, the petcocks will only flow fuel in the Prime ("PRI") position (lever pointing straight back). Also be aware that the Prime position pulls it's fuel from the Reserve stand pipe, so if you run out of gas, you will be really out with no back-up.

Yes, I was told that there was some issue with the fuel tank and its vaccum so im sure this is the issue since the petcocks do have another smaller nipple on the back of them but I don't see any place for them to go on the intake manifold
 

5twins

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Yes, the old intake manifolds on your model had no vacuum nipples. Vac nipple equipped manifolds didn't come along until '78, when the vac petcocks came out. They're very hard to find. An easier option would be to change the petcocks to the manual type. They make special ones to fit that later tank. The mounting screw spacing differs from the early tanks and petcocks so one from an older tank wouldn't fit.

In the Prime position, your vac petcock is effectively "on". If the bike was parked that way, that could explain why the fuel leaked into the engine. A float needle and seat assembly in one of the carbs probably didn't seal completely, allowing fuel to keep flowing in. The float needle and seat assembly really isn't designed to be an absolute "off" valve, more of just a metering valve to control the fuel level as the bike runs.
 

Silviculturalist

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Yes, the old intake manifolds on your model had no vacuum nipples. Vac nipple equipped manifolds didn't come along until '78, when the vac petcocks came out. They're very hard to find. An easier option would be to change the petcocks to the manual type. They make special ones to fit that later tank. The mounting screw spacing differs from the early tanks and petcocks so one from an older tank wouldn't fit.

In the Prime position, your vac petcock is effectively "on". If the bike was parked that way, that could explain why the fuel leaked into the engine. A float needle and seat assembly in one of the carbs probably didn't seal completely, allowing fuel to keep flowing in. The float needle and seat assembly really isn't designed to be an absolute "off" valve, more of just a metering valve to control the fuel level as the bike runs.

Awesome that's really helpful! I dont know how long that would take me to figure out with just google. Do you have any specific recommendations for new manual petcocks?
 

Jim

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Forgive my ignorance but I cant seem to find anything that looks like an ignition condenser? We already swapped the leads and plugs to the working side to make sure they worked and they do.
It's on the top engine mount. Round metal case has both condensers in it. One lead out each end... one for each iggy. Swap the leads to change sides. A dead condenser will kill the iggy just as sure as a coil will. Your mechanic's ever work on a points system or is electronic iggy all they know?


PXL_20210911_155417862.jpg
 

Silviculturalist

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It's on the top engine mount. Round metal case has both condensers in it. One lead out each end... one for each iggy. Swap the leads to change sides. A dead condenser will kill the iggy just as sure as a coil will. Your mechanic's ever work on a points system or is electronic iggy all they know?


View attachment 197948
Okay I found it and swapped the leads, still no spark on that left side
 

Jim

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Okay I found it and swapped the leads, still no spark on that left side
Disconnect the coil lead that goes down to the points.
Take the (disconnected) wire coming out of the coil and touch it to ground a few times. Touching it to ground charges it... the coil.
When you pull it off of ground, the coil should discharge and spark the plug.
 

nj1639

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Awesome that's really helpful! I dont know how long that would take me to figure out with just google. Do you have any specific recommendations for new manual petcocks?

I'm running a Standard '78 xs750 knee dent tank and I have a '78 Standard xs650 tank that I can swap out as the mood fits. Both tanks have the same petcocks pacing so the petcocks are shared between the two. My '77 tank that came with the bike, rough and rusty, has a smaller spacing by about two millimeters. If you decide to go manual then get petcocks for tanks '78 and newer. I purchased one some years ago from bike bandit when they weren't available at mikesxs. It was dual input, required a base and was pricey.....being used on a set of bs34 T linked single input carbs. Most recently in the past few years I got a couple through Amazon, I believe....for a pair of bs38 individual input carbs.....thinking around forty bucks a pop. Still working fine.
 

5twins

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This is the simple coil testing procedure outlined in the factory shop manual .....

zMt0Jeb.jpg


Your coil probably won't have a red/white wire coming out of it but rather a brown one. The red/white is the color of the wire from the harness that connects to it.
 

gggGary

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Leaving a points ignition set up key on when the engine isn't running can burn out a coil.
Literally had a mushroom cloud of smoke leave a Kawie coil while I was trouble shooting one time. Sure wish I had a video of that.
 

MaxPete

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Okay I found it and swapped the leads, still no spark on that left side

Hi Silviculturalist - welcome from Canada's sunny southern coast in Windsor, Ontario!

Please do not get discouraged - these bikes are pretty simple and very reliable and durable so you will get there. You are certainly already talking with the best mechanics on the forum so stick with them - but I will put my oar in here too.

The fact that you have a dead spark plug may be something even simpler than a problem with the wiring harness and the ignition points etc.

The connection at EACH end of the big thick 7mm diameter spark plug wires is not what you'd likely expect. In fact, the big fat spark plug wire screws onto what looks a lot like a big wood screw inside the spark plug cap AND inside the big high voltage terminal on the coil (see the photo below). That ribbed cap on the coil will unscrew and you will see what I am talking about. If either end of that big wire is not properly connected, you will have a dead or intermittent spark on that side.

Inside each of those connections is a sharply pointed tapered screw - and to make a good connection, you must:
  1. carefully strip about 1/4" of the insulation from the end of the spark plug wire;
  2. splay the wires out radially (like rays of sunshine);
  3. screw that splayed out wire end INTO and ONTO the spark plug cap and INTO and ONTO the coil connector (i.e. pushing and turning on each connection at the same time and then repeating at the other end of the spark plug lead).
Don't forget to slide the little ribbed plastic cap (visible in the photo below) and the little ferrule sleeve onto the wire at the coil end - and also - the little rubber boot over the wire at the spark plug end before the "pushing and screwing" ( ;) ) operation. A little dab of dielectric grease may be a good idea too as it will keep moisture out these important connections.

I apologize for not being able to illustrate my thought better - but my wife and I are moving in the coming week and all of my parts are packed and I cannot find a decent photo on the web - but I know that 5Twins, Gary, Mailman or Jim will have one.

Anyhow - making those connections better may very well at least help with, or even cure your dead spark problem.

Cheers,

Pete

s-l300.jpg
LB05EZsparkplugcap.jpg
 
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MaxPete

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Yes, here's how I like to prep the ends of my spark plug wires, and where I like to apply the dielectric grease .....

VqkZjYD.jpg


J8LBimR.jpg
BINGO!!
I knew that someone (often 5T) would have the correct photo.

Silviculturalist: if I were you, before I did anything else on that bike - I would check the connections on the high voltage spark plug lead.

This is a very easy task and well worth doing IMO.

Pete
 
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Silviculturalist

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Alright dropping in to give an update, been very busy between work and other things.

I put in a new ignition coil on the side that wouldnt spark and no more misfiring! So i'm making progress. Now it seems the one side is running very poorly, theres smoke coming from the exhaust, and the other side is running very hot. Previous owner told me he had one side set kind of lean so i'm assuming that may be the issue on the side that gets much hotter. But i've never done much carb work and i've never touched an engine with more than one carb so i'm lost on how to approach this.

The bike also dies when I shift into first gear, I would assume that points towards a clutch issue but I wouldnt really know where to start diagnosing that kind of issue.
 

Adamc

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Like you I had never done any carb work. However I did completely rebuild my BS34 carbs with the correct rebuild kit. Be patient and look at plenty of Youtube videos and research this forum. My 'Welsh Flat Track Revival' thread may encourage you. Use good quality tight fitting tools; and don't over tighten any screws or bolts; carbs strip threads easily.
Read the following several time and use as a starting point. It worked for me straight off the bat!
Screenshot 2021-09-15 at 10.05.33.png
 
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