News:

         
Welcome to FJowners.com


It is the members who make this best place for FJ related content on the internet.

Main Menu

Low RPM Power Problems, Carb Tuning or Ignition?

Started by robertodonnell, March 07, 2021, 03:50:28 AM

Previous topic - Next topic

robertodonnell

Hi everyone,

I have an 1984 1100, it struggles to pull out of, and sometimes even won't pull out of anything under 2500 revs. If I am tooling about town I have to use first gear on slow corners to safely accelerate out of a turn. Once the engine hits 2500, it kind of starts to climb and if I can get it over 3000, it is fine. It is actually a bit like riding a 2 stroke hitting power band.

I have been reading about mixture screws and have set at 2.5 turns out and the blip test is all good, but I have tried going leaner and also richer and I have had no success either way, in fact it is worse so I am pretty sure mixture is spot on. Needle valve clip settings are at second from lowest  (standard I think?), I have rebuilt the carbs, set floats wet as per spec, new plugs and checked valve clearances. Headers are stock and I have a Delkevic centre box and Staintune pipes. All jetting is as per stock.

I really don't know what to do next, apart from take it somewhere, which I would rather not do. There is no stumble, pop or backfire, just a bog down and no acceleration. It is worse in taller gears, but I am still having terrible rideability problems in lower gears as I stated above.

So, where do I look now? Is it possibly ignition advance or some other ignition fault? Possibly too much timing at lower revs causing poor combustion? Or is it likely to be in the carbs still?

I would really appreciate some input, I am racking my brain!

Cheers,

Rob from Oz.

Motofun

Try dropping the needles, clip in second from top.
'69 Honda Trail 90
'75 Honda CB400F
'85 Yamaha RZ350
'85 Yamaha FJ1100
'89 Yamaha FJ1200
'09 Yamaha 125 Zuma
'09 Kawasaki KZ110 (grand kids)
'13 Suzuki GSXR 750 (track)
'14 Yamaha FZ-09
'18 Suzuki GSXR 1000R (track)
'23 Yamaha Tenere 7
SOLD: CBX,RZ500,Ninja 650,CB400F,V45 Sabre,CB700SC,R1

Pat Conlon

Yes, what Jack said ^^^ If your needles are now set "second clip from the lowest" try moving the clip to the middle notch or 2nd from the top. The lower the clip (from top of needle) the higher the needle is raised and more fuel you get...

You have Low rpm bog from flooding....other things to do...check your float bowl fuel levels...Too high? lower your floats...replace your float needle seat o rings. Check float needle and seats for wear. Replace if needed.
Check the needle opening in the brass needle jets (aka emulsion tubes) for ovaling, replace if needed.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

fj1289

Can you fill in some background info?

Is the bike new to you?  Has it always run like this?

Or have you had the bike for a while and it has always run well and this s a recent development?

Has something been worked on or changed recently?

Don't  want to suggest jetting changes if the problem is dirty or clogged up jets or passages in the carbs.   

Also, how is the battery? 

krusty

Seems like the carbs need a thorough clean, especially the low speed system.
91 FJ1200
84 FJ1100 x 2
85 FJ1100
89 GL1500
76 CB750F1
72 CB350F
63 C92 x 2
59 C76
62 C100
63 C100
60 Colleda 250TA x 3
63 Suzuki MD50
77 DT125E
77 DT175E x 2
79 DT250F

Old Rider

I would try to pull the choke while riding under 3000rpm if it runs better and pulls away  it is too lean .I guess you already checked the airfilter but if not check it. Take a look at the sparkplugs if they are too clean / white deposits it is  too lean.

Waiex191

Mine rode like that until I got the low speed system sorted out.  I just had two carbs plugged.

http://www.fjowners.com/index.php?topic=19343.150
Bryan
1989 FJ1200
1981 Suzuki GN400
Poplar Grove, IL
 

FJ_Hooligan

Quote from: Pat Conlon on March 07, 2021, 05:50:12 PM
You have Low rpm bog from flooding....other things to do...check your float bowl fuel levels...Too high? lower your floats...replace your float needle seat o rings. Check float needle and seats for wear. Replace if needed.


That Pat guy is pretty smart.  I've seen this exact behavior when the fuel level was too high.  Idle and initial takeoff were ok, but twist the throttle and it was like pushing a wall.  It would eventually get though with slight throttle inputs.  On the other side, it ran great.
DavidR.

robertodonnell

Wow guys, thanks heaps for all the great replies!

I had already decided it was a rich state problem because I did the choke test and it got worse, I was just unsure of how to go about it.

The bike has been with me about a year, and it's never been a fully tuned running example until now. It has been through a lot and I don't think the previous owner even rode it.

I dropped the needles 2 clicks (circlip now one groove from the needle top), and it's incredibly better now. The engine pulls well from top gear at 2000 revs, but still lacks enough torque to use top gear under 2000 revs.

Should I look at dropping the needles another click, tightening the mixture screws (which are at 2.5 turns), or would I need to check the float levels again? It still seems fat when you roll the throttle on under 2000, and then once it hits the magic 2k it starts to run clean and accelerate well.

One thing I can tell you is that the choke isn't much help when the engine is cold. I was under the impression that with the choke open cold it would increase the engine's idle enough to get it over the 1100 revs it's at hot, but it struggles to get over 800 revs and then about a minute later it's choke off or the engine is stalling, and I need to wait a little before the engine is up to the challenge of idling on its own.

Cheers,

Rob


Motofun

The "choke" is actually an enrichener.  It doesn't impede air, rather adds fuel.  The bore holes are TINY and there are one in each carb body.  When you put the "choke" on you should be pulling each enrichener equally.  They have a history of slipping on the pull rod and/or the brass head on the enrichener can wear out and fail.  All four need to work for the cold start to work as it should.
'69 Honda Trail 90
'75 Honda CB400F
'85 Yamaha RZ350
'85 Yamaha FJ1100
'89 Yamaha FJ1200
'09 Yamaha 125 Zuma
'09 Kawasaki KZ110 (grand kids)
'13 Suzuki GSXR 750 (track)
'14 Yamaha FZ-09
'18 Suzuki GSXR 1000R (track)
'23 Yamaha Tenere 7
SOLD: CBX,RZ500,Ninja 650,CB400F,V45 Sabre,CB700SC,R1

robertodonnell

Yes I did take a good look at the choke valves when I rebuilt the carbs. There is some wear on the plungers where the external gang of forks pull the plungers out, but I was confident at the time I installed them that they were all working in unison.

Old Rider

If you measured the float height with the carbs upside down and the small spring in the needle is a little weak the fuel level can be too high in the emulsion tubes / bowls.
Making it run too rich

robertodonnell

No I set the floats wet. But I may not have used the right inclination angle on them when I did it, so it is possible it's a tad high.

FJ_Hooligan

How do the plugs look?

When you rebuilt the carbs, did you replace the o-rings on the needle seat assemblies?

When checking the fuel level, you don't need to worry about the angle as long as you measure at the middle of the float bowl.  Better to err on the lower fuel level.

As Jack said, the choke is an enrichener.  If the choke fuel orifice in the side of the float bowl is clogged, the choke will make cold starting even worse.  Also, the forks that pull the choke plungers are all alike except for the fork on carb #1.  That fork has an offset.  Make sure the offset fork is on #1 otherwise it's trouble.

For best setting on the mixture screws, perform the "blip the throttle test."
DavidR.

robertodonnell

Yes all the O rings were replaced when I did the carbs. The choke galleries were all clean and free, and all the pistons move well.

I read somewhere that I could cut fuel supply to the carbs and see if the running improved. It did not, and while I was doing this I came to the conclusion that I may have a lean state in the lower revs...

What I did do to find the issue was to open the throttle to 1900 revs and while the engine was running unhappily, I screwed the pilot screws out until I got it running nicely. This was at 3.5 turns, and then I went for a ride. I have it running much better now at lower revs, but I but  I now need to revisit the needle valves as I enthusiastically lowered them one more step and I got a lean state at WOT around 7000 rpm.

We are in for a week of terrible weather, so I won't be doing any tuning runs this week it would seem. Once I do the needle reset I am going to read the plugs again. I was getting very black sooty looking plugs, which is why I thought I was running too rich.