1984 VF700F exhaust on one side is cold???

Discussion in '1st & 2nd Generation 1983-1989' started by 74ullc, Aug 6, 2014.

  1. 74ullc

    74ullc New Member

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    At idle the right side exhaust gas is cold....left side is hot. Feels like equal pressure on each side, both sides seems to be breathing equally. All four pipes right out of the engine are hot and collector under the bike is hot but 6 inches after the collector the right side pipe feels just warm, not hot like the left side.

    I cant for sure hear a miss when I hold the throttle at a steady 3K. Bike seems to idle just fine but I assume it could with just 3 cylinders firing.

    I haven't changed the plugs yet, no idea how old they are. I did check all 4 wires with a timing light to be sure there was spark on all 4 and there was. However I don't think that would tell me if a plug is bad and grounding internally.

    I know the obvious, change the plugs and see what happens. Also I did just remove and clean the carbs but I realized after I got them back on I made a rookie mistake! I did not remove the mix screws and shoot cleaner thru there while I had the carbs off. I did remove all the jets and blow thru those passages but without removing the mix screws realize I could have just packed some crud in there.

    Mix screws are all set within a quarter turn of 3 turns out. That's were they were when I got the bike. I will go thru the setting procedure in the manual but need to get it firing on all 4 first. I have not tried turning them to see if they have an effect on idle speed.

    My main question is why would the exhaust be hot on only one side? Is the collector not just a hollow space where gas from all 4 mixes and then goes out the mufflers?

    Pics of bike are here.....since everyone like pics.....

    http://vfrworld.com/forums/showthre...1-more-1984-VF700F-back-on-the-road-hopefully!
     
  2. fastenough

    fastenough New Member

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    i have to give you a bump :) i noticed the same thing on my 86 500, hope someone can answer
     
  3. 74ullc

    74ullc New Member

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    Same thing on yours huh? Does it run ok? Running on all four?

    I figure its due to missing on one or more cylinders, on my bike that is. But its the collector that makes me wonder how one side could be cold and one hot if all the gasses from all 4 cylinders are mixing in the collector. That's what I was hoping someone could clarify.....maybe the collector isn't just a hollow box but has crossover tubes or something like that in it?
     
  4. squirrelman

    squirrelman Member

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    bingo !!!!!!
     
  5. 74ullc

    74ullc New Member

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    Do you know which cylinders feed the right side exhaust? Right side as when viewed from the rear of the bike.....the view HD riders will have once its running correctly.
     
  6. MPH Racing

    MPH Racing New Member

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    My original had rusted out inside so I cut it open to see if I could fix it. The front 2 cyl come straight into the box but the back 2 go into tubes that cross over inside and make an S bend (probably to make the the same length as the fronts) and return to facing the muffler on the same side. Before I changed it (woot E-bay) the Left side muffler was running cool and the Right side ran warm and felt like the Left side was only running 1 cyl. After I changed it the exhaust sounded more balanced and the exhaust feels about the same temp.
     
  7. 74ullc

    74ullc New Member

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    So left cylinders feed left pipe and right cylinders feed right pipe? The rear pipes do an S bend inside the collector but still come out the same side?

    Just trying to get an initial idea of which cylinder to look at that could be missing. All 4 exhaust collars seem to get hot quickly so I was wondering if the cool exhaust on one side could point me in the right direction. But it sounds like not really.....sounds like cool exhaust on one side can be caused by other things.

    I bought new spark plugs to try first, just been very busy this week and haven't had a chance to dig into it yet. Betting its going to end up being carbs.
     
  8. ThatVF500Guy

    ThatVF500Guy New Member

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    Hi David, Have you compared temps at the header pipes? My H1 had the same problem. One pipe would not heat the same as the other two. I traced it to a pilot circuit issue in that carb. If the carb for that cylinder is not functioning properly it can cause that cylinder not to heat up. If you have an infrared heat sensor you can get a pretty accurate measurement.
    Good luck,
    Jim
     
  9. squirrelman

    squirrelman Member

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    Just as that guy ^^ sez, likely problem (if it's not spark-related) is cloggted slow jets or mixture screw passages in carbs.
     
  10. 74ullc

    74ullc New Member

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    As far as temp goes, all I have done is feel the exhaust collars at startup from cold. The right rear collar seemed to take longer to get hot than the others. But that's on the left side and the cool exhaust is on the right. Unless the rear pipes crossover in the collector, then it would make sense.

    I don't have an infrared temp gun but this is not the first time I have needed one. Next trip to Harbor Freight I'll get one.

    What you guys are saying about the carbs is probably true.....I did take them off and clean them. Bike didn't run when I got it, quick carb clean got it running. But I did do a quick job and like I mentioned.....I completely forgot to remove the mix screws while I had the carbs off!

    I was in a hurry and didn't realize I did that until after the carbs were back on the bike. So....I could very easily and most likely have clogged mix screw passages. I sprayed cleaner thru all the passages but with those screws still in place I could have just packed crud up against them.

    I have new plugs and I'll try that first....eliminate ignition problem first but since both the fuel pump and the tach work I think both black boxes are ok. I haven't check compression either, I could have a dead cylinder.

    On another note....my KZ is running great! I moved the Honda up to the front of the garage and put the KZ by the door....for now anyways. The idea is to get the Honda running and save some miles on the KZ.
     
  11. fastenough

    fastenough New Member

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    i did the same thing (cleaned carbs without cleaning mix screw holes)

    is it possible to back the mixture screws all the way out with the carbs on the bike, spray, and re-install?
     
  12. ThatVF500Guy

    ThatVF500Guy New Member

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    It is but you should remove the o-ring as well. It's easy to lose teh washer too so you ahve to be careful. Best to do it with the carbs off the bike so you can apply a little compressed air.
     
  13. 74ullc

    74ullc New Member

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    Finally got around to pulling the carbs back off, been busy with work and just haven't had time to mess with it. But had a few hours today. Carbs came off a lot faster the second time!

    I pulled the mix screws, washers and o-rings this time and found a piece of what looks like grass or insect shell in carb #3 behind the mix screw. It had the port plugged up so HOPEFULLY I found the problem. I'm still a little confused if #3 cylinder exhaust is on the left or right side. Its the rear/right cylinder but not sure if the rears crossover inside the collector or not.

    If cylinder 3 does exhaust out the right side then that could explain the cold right side exhaust. We'll see....I'm going to give the carbs another good cleaning while they are out even though they look spotless other than behind the mix screws. All 4 had a little crud in there but only #3 seemed to be restricted.

    I'll report back once the bike is running again.
     
  14. NAVMAV

    NAVMAV New Member

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    I have the same thing going on with my '85 VF500F. But if you touch each header pipe coming off the cylinder,... they are all hot. No clue.
     
  15. NAVMAV

    NAVMAV New Member

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    Hello,...my '85 VF500F was and still is doing the same thing. mildly warm exhaust off the left side,... hot on the right. The header pipes coming off each cylinder are all hot. New carbs pre adjusted and drag pipes. I'm not sure why the header pipes get hot and not transition thru the left pipe. Anyway,...Just thought I would share.
     
  16. Dukiedook

    Dukiedook New Member

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    You sure that muffler isn't plugged with mice or squirrel goodies?
     
  17. 74ullc

    74ullc New Member

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    No I'm not, and with only 10,550 miles this bike must have done some sitting at some point. When I got it, it had been at least a few years.

    I will remove the muffler and take a look, but both sides seem to have just as much pressure, just one side is cold.....or only slightly warm, it really feels like a warm/cold/warm/cold.....like one cylinder not firing. I can hold my hand over the end of the muffler no problem, the other side.....no way....it will burn you.

    I have the carbs off now and am about to finish cleaning them and re install and maybe even get a test run in tonight. New spark plugs going in also.
     
  18. 74ullc

    74ullc New Member

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    Got the carbs back on. Seems to 'maybe' idle a little smoother but the right side exhaust is still cool. All four exhaust collars seem to get hot very quickly. As far as pressure goes, if anything the right/cold side is blowing harder, I can feel it further back from the bike.

    So I dunno. I still hear a miss in that right side when holding the throttle at 3k too. So I still have work to do.

    I pulled the plugs and changed to new ones while the carbs were off. The plugs on the left side cylinders looked perfect. On the right, the rear cylinder was really wet with fuel and the front was maybe a touch wet. I will have to pull the new plugs after a little running and see if the results are the same.

    Moving the mix screws on all four carbs individually does change the idle so I know the passages are clear. The screws were set at...

    Cylinder #1 LR = 3.5 turns
    Cylinder #2 LF = 3.25 turns
    Cylinder #3 RR = 2.875 turns
    Cylinder #4 RR = 3.25 turns

    I set them all at 3 turns for now and will use the book method to set them and see what I get.

    I don't think the problem is coils since that would be either the fronts or the backs but not a front and a rear from one side. Could be the wires or caps.

    Two things I have not done are check carb sync, and a compression test. When I had the carbs out I could tell by eye that they were not all exactly even when closed, very close but not exactly the same. But they most likely wont be even if they are vacuum synced correctly so I left them alone for now.

    I have vacuum gauges but what do I use to hook them up to the engine? I see the little ports on the intake, is there a special tool? On my KZ its a barb for the hose built onto the carb holder, Honda is not like that. I figure there is a screw in barb fitting or something?

    As for compression, I really wanted to check that when the carbs were off but I couldn't find the correct size to fit the plug hole. Apparently these plugs are an odd size? What are you guys using?
     
  19. JasonWW

    JasonWW New Member

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    I just skimmed this thread, but I didn't see anyone mention it's probably because your carbs are a little out of sync. A quick test is a cold start with the throttle cracked open just a little. That one cylinder that's not getting enough air will kick in and it will get warm like the rest.

    I had the same issue of one cold pipe at idle. Nothing was wrong and the bike ran well. Just do a good sync with a warm engine and it should go away. No worries!
     
  20. NormK

    NormK New Member

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    Rear plug wet, front plug a little wet, those plugs are not firing if they are wet
     
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