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Old 12-02-2017, 07:26 PM
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thumperjsa thumperjsa is offline
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Gremlin - power struggle at around 4.5K and up

Gonna just throw this out there at you guys. Recent issue where in lower gears (1 and 2) it seems the motor is having problem developing power above 5k. Not trying to go 100 MPH so didn't test in above gears. When in Nuetral, no issue to get above 5k. So just under load.

Seems to bog down like it can't go more and can often fight to a little higher by opening throttle a bit more. I can get to near 45 MPh in first OK, but hard to get above that for example.
First, items changed and checked since problem developed.
Replaced with new Dynatek coils and wires, been wanting these anyway.
Replaced battery
Checked pickup wires and vacuum advance. All hoses for vacuum appear to be OK.
Checked carbs that they are balanced
After trying to run through 5k, checked plugs. All look what I would label as a shade of tan.
Checked voltage at several points like coils and looks good to me from all I see.

So what else should I check. I'm thinking maybe something is up in the carb. Floats? I am planning to pull the carbs off next weekend to go through them. But before I do, looking for ideas/advice before I yank them out.

One item of note. Since the new Dyna coil went in. I can get above 5k but still bogs a lot at around 5k and it takes time to develop power above 5k.

Alrighty, please discuss and help me find this gremlin.
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Old 12-02-2017, 09:06 PM
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Battery voltage is ?? Voltage at coils is ?? You my be dropping some electrons along the way.
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Old 12-02-2017, 10:52 PM
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1. Put in clean/new plugs. Take it out and go as hard as you can in 2nd until redline, then kill the ignition. Coast to a stop with the clutch in, and remove a plug or two and check. My guess is you are running lean because of float level or main jet with something in it. It could also be caused by a hole in the slide diaphram, not allowing it to raise as it should.
2. check that the advance unit is smooth and does not hang.
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Old 12-03-2017, 01:13 PM
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Did you put they pilot jet plugs back in the carbs? I did that once, seemed to run best until 5k, then no power.
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Old 12-03-2017, 03:19 PM
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Hey there,

Can't recall any intake mods you have, like pod filters vs. OEM airbox? But if you DO have pods, try taking them off and see if you can get it above 5K easily, if so, then you have restriction from the pods and intake ports. See tech tips regarding mods for that.

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Old 12-03-2017, 05:32 PM
motoman motoman is offline
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Quote:
Originally Posted by jetmechmarty View Post
Battery voltage is ?? Voltage at coils is ?? You my be dropping some electrons along the way.
Totally agree with you on that one Marty!
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Old 12-04-2017, 06:03 AM
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Did you perform a carb sync?
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Old 12-09-2017, 03:48 AM
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Thanks for the tips guys. Been offline and haven't been able to check back in to the XS site. Just wanted to let you know I'm not ignoring. I'm going to try and look at some of these things this weekend.

Just some answers.

Yes, checked the carb sync and it seems fine. I'm not using oversized jets or pod filters, just an unmoderated original setup. Also just to clarify, this is a 1980 bike with 79 carbs. Been this way since I bought it many, many years ago. I replaced my jets with original Mikuni after running some off brand I got a year or so ago. This situation is recent so I don't think that's the issue either.

I was checking the voltages but my meter was freaking out and giving me a reading all over the place. So I've got a different meter to test with. I just replaced the battery though because it was dying on me. But I'll check those voltages again.

I also checked the mechanical advance. It's not sticking at all and it seems to be operating fine as accelerating shows the vacuum advance is moving.

Since the swap to dyna coils I can fight through to 6k, but it's a fight through like it's struggling to accelerate. With testing everything else out, I'm thinking something in the carbs. May need to just take them apart again and see what's up. Last thing I did to them was replace the Fuel Ts as they were leaking a bit. Maybe something went haywire from that change out. But as I said, the pressures for the carb sync looked good.

Although floats sounds like it could be an issue. Maybe the change out of the fuel Ts and flipping the carbs over during the fuel t swap out did something to those. Odd though because I'd think I'd see fuel starvation at lower RPMs too. The new Fuel Ts I got looked fine. I am running external fuel filters and maybe they could be affecting it. It's been a while since I changed those.

Just curious, at full throttle how long would it take to burn through all the fuel in the float bowl? Wondering about fuel flow effect at full throttle.
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Old 12-09-2017, 08:58 AM
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Quote:
Originally Posted by thumperjsa View Post
I am running external fuel filters and maybe they could be affecting it. It's been a while since I changed those.

Just curious, at full throttle how long would it take to burn through all the fuel in the float bowl? Wondering about fuel flow effect at full throttle.
Well, having 79 carbs can make everything less complicated. At least you don't have one of the 80 transitional carb sets! You of course need to set the floats for the 79 vintage. I have never had any luck with the small fuel filters that have the porous stones. They just don't flow enough fuel. If you don't have issues with the pick-up wires, and you have new HT coils, it sounds to me like fuel supply. Fram makes an in-line metal filter that is narrow diameter and works well for me. (#g3515 I think). Have you tried running on Prime to rule out any issues with the vacuum operated petcocks?

You asked about drawing down fuel at full throttle. Once the level drops below the main jet, the bike will die. You can draw it lower with the "choke" but if you open the throttle, the choke becomes less effective because you kill vacuum. The choke circuit (enrichener) draws fuel from the bottom of the bowls.

I would think fuel supply is the problem (or very lean float height).
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Old 12-09-2017, 11:17 AM
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I forgot if you have slight rust spots inside the gas tank or on the inner fuel cap?

That gritty rust debris can clog up those in-line filters really easily and you mentioned you haven't changed them for awhile.
clogged, btdt till i put in the Caswell Blue tank liner.

Skids may have nailed it .........................

New fuel filters, now that would be an easy fix. Hope in your case you get the simple repair.
Got to be ready for the Florida Rally in February. not that you will be needing 6,000 rpm on that ride.

Jeff
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  #11  
Old 12-11-2017, 03:59 PM
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Didn't get to do anymore diagnosis this weekend. I'm curious though before I look at the carbs or fuel filter to try opening up the enrichment and see how that effects it at high rpm though.
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Old 12-11-2017, 04:31 PM
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How about valve out of adjustment, could that cause a high RPM struggle?
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Old 12-11-2017, 07:21 PM
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A possibility since I haven't checked valve clearances for years.
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Old 12-15-2017, 10:30 PM
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Hey again,

Okay, No Pods, OEM Mikuni jets, ignition parts under side cover working.?
The timing plate movement with the vac. adv. is just one part of the timing advance process. The other is the plate moving with the centrifugal mechanical parts spreading out as rpm's increase which also rotates the timing plate, but you can't see/tell it without a TIMING LIGHT. SO...you'll want to plug off the vac. adv. and then use the timing light on #1, and see that the timing indicator rotates to ~35 degrees BTDC at around 5K rpms. IF it doesn't, then you'll need to take off the parts, clean/grease and reassemble and then recheck.

Replaced OEM coils with Dyna's, forgot to ask if you bypassed the Ballast Resistor, and are they the 3.0 ohm Dyna's, or the 1.5 ohms type?

Also have you verified that you ARE getting spark on all 4 plugs, and have the wires going to the correct cylinders, 1-4 and 2-3 paired, and not mispaired like 1-2 and 3-4? No aspersions on your skills, but have seen/heard of some interesting faux paux's.

T.C.
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Old 12-17-2017, 10:15 AM
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If the valve clearances are out of spec, there is nothing downstream that you can do to correct the results of the valve clearance problem.

After you adjust the clearances, use a hanging fuel bottle and bypass the fuel filter(s) for the tuning process.

Does it bog down at 4500 rpm when you are in neutral or just under load on the road?
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