stutter at WOT (only in 5th)

[ocatoro]

Just done 100 mile round trip to swansea, bike was fine on the way there. But on the dual carriageway on the way home I had a feeling like the bike was braking. the odd stutter like this. particularly up hills, which caused excessive loss of speed then.
This was also apparent then on the country roads for the second half of the 50 mile home journey up the steep hills, again excessive loss of speed.

The bike is a 1986 Honda H100 SII.

I thought, ah it's cold, maybe it's carb icing. Or perhaps there's just a slight intermittent blockage, but wouldn't that be apparent on heavy acceleration too? And in all gears I'd have thought, rather than just in 5th.

Gearbox has plenty of oil, and the electrics appear to be functioning properly.

What does BCF think is going on here?
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CBT - 17/09/12 * Theory - 23/10/12 * Mod1 - 05/03/13 * Mod2 - 25/03/13 * BOSH!
Current - None but shed project H100 (first bike )
Past - ER5, '93 ZZR600, '92 CB400 SF, ZZR600 (again), yellow Monster 620, Blackbird - black Monster 620ie - '96 ZZR600

[numpty2]

Carb icing tends to happen more at wider throttle openings. The more air & fuel that is going through the carb, the colder it gets. There is a fuel additive that prevents it, Silkolene PRO FST.

But is it really cold enough yet? My bikes have suffered from carb icing, but only when riding below 3-4°C in early mornings in frosty air.

It may be carb related, not enough fuel getting through to keep up with the engine, but I doubt it is carb icing.

[ocatoro]

ok thanks, yeah it's been fine in much lower temperatures, it was just a thought.

I'll open the carb up tomorrow and give it a good clean, see if that helps.

it's very odd that it's only in top gear though isn't it? i held it in 3rd and 4th at the same rpm and WOT to push through, but nothing. only in 5th.
____________________
CBT - 17/09/12 * Theory - 23/10/12 * Mod1 - 05/03/13 * Mod2 - 25/03/13 * BOSH!
Current - None but shed project H100 (first bike )
Past - ER5, '93 ZZR600, '92 CB400 SF, ZZR600 (again), yellow Monster 620, Blackbird - black Monster 620ie - '96 ZZR600

[numpty2]

I'd be inclined to check a few other things before taking a carb apart. Some carbs never go back together properly.

Maybe:
Check the fuel filter - a blockage would limit fuel flow
Air filter - clean or replace
Spark plug - check, probably replace

I tend to just replace spark plugs nowadays. You'll want to get one in case it needs changing, so why not just fit a new one anyway. It all depends on how old it is. If you're not sure, assume it needs replacing.

Some of these little engines can be sensitive to the type of plug, hotter/colder grades etc. Have you checked to make sure you have the correct grade in at the moment?

[ocatoro]

ok cheers bud
____________________
CBT - 17/09/12 * Theory - 23/10/12 * Mod1 - 05/03/13 * Mod2 - 25/03/13 * BOSH!
Current - None but shed project H100 (first bike )
Past - ER5, '93 ZZR600, '92 CB400 SF, ZZR600 (again), yellow Monster 620, Blackbird - black Monster 620ie - '96 ZZR600

[cb1rocket]

Ignition coil breaking down usually. I had the same problem, replaced and fixed mine ok

[numpty2]

Yes to the ignition coil suggestion. On a simple bike like this I'd be inclined to change the HT lead & plug at the same time. It's all going to pretty cheap.

You may not have much power on a H100, but you are still laughing all the way to the bank compared with pretty much any other way of getting around.

Touching the carb would still be my last choice. Carbs are very reliable, whereas coils & HT leads do wear out. It may even be on the original coil & HT lead.

[numpty2]

Ignition coil is pretty cheap, and the image suggests it comes with HT lead:

https://www.wemoto.com/bikes/honda/h_100_sg_sj/86-93/picture/ignition_coil/

So £20 for the coil, few quid for a new spark plug.


The spares sites show a foam air filter, so that might benefit from a clean.

So a bit of TLC for the old girl, and you will continue to potter around for next to nothing. These old bikes can be run on a shoe string. And remember to change the oil very often since they have a small oil capacity.

[cb1rocket]

https://www.ebay.co.uk/itm/Baotian-T9-T2-T12-Jinlun-Jonway-BTM-125cc-IGNITION-COIL-/190742734388?pt=UK_Motorcycle_Parts&hash=item2c69272634

The one I linked is the one you need. It's funny that all the major shops are listing the wrong coil unless yours is the SD model

[cb1rocket]

https://www.ebay.co.uk/itm/GENUINE-HONDA-IGNITION-COIL-for-H100S-PART-NUMBER-30510-GG2-710-/281013484621?pt=UK_Motorcycle_Parts&hash=item416db57c4d


Genuine one if you fancy just paying for the name.....

[monkeyman]

The fact the stutter is only present in 5th should indicate that it is not a ignition problem. Because if the ignition was faulty it would be present in all gears

From the ignitions point of view there is no difference riding at wot in 4th or 5th

First port of call would be a fueling issue for symptoms you are describing.

Change your fuel filter first if you have one
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Im not the best, but im in the top one
RM 250, Husky TE610, K1 GSXR 750

[JonnyFoxtrot]

I would be pointing at a fuel problem.

Probably carb and probably mixture related.

So I'd be thinking blocked or dirty jets, especially as its only WOT and that would lead me to point the finger directly at the main jet as WOT is its main job.
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'89 Honda NS125F (SOLD) -> '92 Suzuki GS500E (SOLD) -> '03 Kawasaki ZX6R B1H (SOLD) -> '96 VFR 750 RC36 (SOLD) -> '02 Honda CBR1100XX Blackbird

[StevRS]

Is it definitely engine? Clutch slip is normally first apparent in higher gears.
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MV Agusta Brutale 800 RR, Unfinished 1978 XS250