Jump to content

Two of four cylinder died


Recommended Posts

I bought a 1978 gs 750 e about a month ago.   Needed it's lights rewired but other than that it was in good shape.   Rode it for a couple days than all of a sudden it bogged down.    I can get the old girl ta start, but she is only firing off the first two cylinders.   Cylinders 3 and 4 don't even get warm.  They are getting fuel, [spark plugs are whet when I pulled them]  and I switched the plugs around to make sure they are ok.    All the plugs work.   I'm certain it's getting compression, but don't actually have a meter to gauge properly.  Have no clue what to look into next, and it's my main mode of transportation at the moment.  Please, if any one could throw some ideas out there.  I'd be very thankfully.  

Edited by Plaid_Bagger
Spelling
Link to comment

have you tried the basics like changing the plugs? doesnt sound lik an ignition fault as the coils are paired 1+4 and 2+3 so an ignition fault on either circuit would take out that pair. but you have one from each pair running which suggests fueling. carbs could be flooding, but tbh there are a lot of other variables that need to be taken into account. so,  compression test first, then if thats ok, fresh plugs, then carbs.

Link to comment

Try swapping the spark plug leads for each coil.

Take 1 and swap it with 4. Swap 2 and 3.

 

Does the problem now move so 1 and 2  aren't firing?

 

Start it up in the dark and see if the spark plug caps are shorting out while its running

 

Does your bike still have points?

Link to comment

So, just to make sure I've got it all ;)

1. All 4 cylinders are getting fuel.

2. Have good compression on all 4 cylinders (above 100psi)

3. All 4 plugs are giving  a good spark.

So if all the above is wright, try 

1. Get 4 new plugs put them in and see, you may have some duff plugs (had this myself the plugs fail under compression but look OK otherwise).

2. Put HT and caps from 1to4 and 2 to 3 see what happens, if it stay with 3/4 cylinders or goes to 1/2. May have 2 bad caps.

3. Check 3/4 cylinder carbs are not flooding, are you running air box or pod filters?

But my bet is on duff plugs, you sometimes find they give a good spark out and against the head but when put in they go coupt. 

  • Like 1
Link to comment

So I switched the wires around.   And still the same.   1 and 2 fired.   Have good compression.   So I tore the carbs out.  Ordered a rebuild kit, going to bench sync the floats again.   Has to be something going on in the carbs.   Was wondering about the t section where the fuel splits off. Thanks for the help guys.  Apprcost a that.  

  • Like 1
Link to comment
  • 2 weeks later...

So it has finally been above 20 degrees and I have been back to playing with the bike.   I started it up out of curiosity and the pipes for 3 and 4 had a little heat to them.   So I took the carbs off and of course the carbs had a bunch of fuel.   So somewhere something is sticking or flooding.   Be working on the rebuilds.  Anything specific I should be looking for?

Link to comment

Have you tried new plugs yet?...I find that plugs nowadays do not tend to last half as long as they used to and they give up the ghost at the faintest wiff of over-fuelling..I find only a good cook in the oven brings them back to life.....

Have you tried increasing/holding the revs and seeing if the warm downpipes get hotter....over fuelling on the idle circuit will wet your spark but could clear with grater throttle positions.Rich at idle could point to sticking float needles.

Link to comment

I have tried at higher revs.  And I think that's how the pipes warmed up.   Bot it bogs out and dies.  I just bought the spark plugs.   And I did buy new one and tried again.  Same thing.   So I'm going to deep clean the housing and the fuel pipe that goes to the carbs.   That link is awesome.  Thank you.   I've done lawn mower carbs.   But this is different.  Like I said, now that it's above 30 degrees during the day I'm able to get some work done.  

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...