GZ125 marauder not revving through

[virus]

this ones baffling me so I thought id ask, first off a bit of back story.

Got a 125 marauder for mrs Virus, bought as a non runner that apparently cut out whilst riding. Done a fair bit of overhauling to it and tidying things up before getting it though MOT. Including replacing the wiring loom that dropped down onto the drive chain and took 10 or so wires back to bare strands (probably explains the cut out whilst riding).

Symptoms:
Wont rev over 6.5/7k (no rev counter on this bike but based off putting the ratios into gearing commander and looking at the wheel speed in a set gear, its not pulling past 7 and should pull to 9/10k)

What I've looked at:
Compression checks out fine at 175psi, should be 140-190
Valve clearances were checked however some twat has rounded the bolt in the cover to turn it to TDC and its got those woeful little inspection ports on the rocker cover that make it a pain in the arse to see what your doing. I just turned it using the back wheel til the lobe was pointing away then did the clearances. This however does mean I've not checked timing lines up with my own eyes.

Carb is a genuine mikuni that looks to be the right one, none of the jets in it had any number stamps on though. Ive set the pilot air screw and float height to factory settings and cleaned the jets.
Given that it wont go over 7k I suspected main jet wrong size so I replaced it with a genuine miki 117.5 (should be 112.5 stock) but this made no difference at all.
Pissing with the choke whilst its stumbling at 6.5k does nothing to improve or worsen the situation.

Wiring loom on the bike did have a connector for a throttle position sensor but this particular carb has no such sensor fitted. I assume from the age of it that this TPS does very little much like the early oil cooled Suzuki stuff made no noticeable difference when plugged in or not.

Spark is nice and strong when rev tested at idle.



I was fairly certain it was carb related and we are going to take it for a ride this weekend and dick around with needle height to see if that makes any difference but I'm wondering if I'm missing something else?
Could it actually be timing and its jumped a tooth?
Could the ignition not be advancing somehow? (cdi not points)

If anyone's got any ideas I'm all ears, She can ride it to work currently as she works local and doesn't NEED to do over 50 but it'd be nice to let her have full use of however many of the 12 horses are still left in it.


Cheers
VJ
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own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[WD Forte]

The tps wasn't put on for fun y'know.
Its function is to advance the spark at wider throttle openings.
They usually work by having two signal inputs on the SCR trigger inside the CDI box..

In normal use the SCR is triggered when a pulse from the fixed pulser
has risen to a pre set voltage.
The tps uses a a few components to make it trigger at a voltage
which arises sooner, ie more advanced, in the cycle of the crank.
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bikers smell of wee

[virus]

Interesting, Ive never had any noticable issues by unplugging them on other CDI and carbed Suzukis of the age.

The curious thing is that the carb on the bike is the 'original' that it came with from previous owner, as is the CDI. the loom itself is one ive swapped in. I may have to look into if 'early' ones had no TPS and 'later' ones do, and ive unwittedly swapped a 'late' loom onto a 'early' but im not sure the CDI ever changed.

Ive got the old fucked loom in the garage still incase I need to rip a block connector out of it so i'll check for a TPS plug tomorrow anyways.

Cheers
____________________
own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[virus]

Well I checked the old loom and noticed it has a TPS connector. The carb on the bike doesnt have a TPS though so im assuming its not the original marauder carb. Further research shows that the marauder engine never had a tacho drive in the head but this one does so I suspect it to actually be engine swapped with another GN125 derivative.

Curiosity got the better of me and I checked the timing, its was 1 tooth retarded so I've reset it. Bit of camchain wear means its a fraction advanced but much better than 1 tooth out. Took it for a test and it starts nicer, sounds less lumpy and rattly. STILL hits a wall at 6k. Pissing around with the choke makes no difference

So now im reading the manual for the section on the resistance settings of the TPS, with the idea of putting a 4k Ohm or whatever is midrange in the spot and seeing if that makes any difference. Maybe no resistance (its open circuit atm) is fine at lower RPM but I might be able to find out what resistance it wants to give the ignition curve a 'compromise' position.

Mostly doing this because there are no cheap TPS carbs available and I want to rule it out before spending too much money.
____________________
own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[Robby]

Variable resistor with an advance-retard lever on the handlebars, if you're looking for a quick divorce.

[virus]

Havent even convinced the daft wench to marry me yet so thats a bit of a challenge.

Ordered the only carb I could find on ebay that is actually a bs26ss with a TPS, Its in bad condition but hopefully I can parts bin the 2 carbs into one decent runner, even if it does possibly mean making a new throttle shaft at work.
____________________
own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[stinkwheel]

Also check your fuel flow. In case it's just getting a dribble through the tap.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[virus]

aye good shout, fuel flow on main both before and after the filter seems sufficient for a gravity fed 125 carb.
____________________
own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[WD Forte]

[virus]

Well now im confused. If the purpose of the TPS isnt to be a variable resistor then why does the manual say to check it by measuring the resistance a 2 set points?
____________________
own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.