Flat spot/lag from closed throttle

[jim280885]

Hey gang.

My bike has a ridiculously frustrating delay when transitioning from closed to part throttle openings (as in EVERY time I start winding hte power back on coming out of corners) it also surges at steady part throttle openings (eg. highway in top) When riding particularly hard and this is happening higher up in the rev range it also pops while it lags. The delay lasts about a 3rd of a second then the power comes back on abruptly. The mech said he balanced the carbs, and when I picked it up I THINK it was sorted, I only really rode it twice and not too enthusiatically, before the carbs flooded and pissed fuel all over the place. We pulled the float bowls off and cleared the inlets then reassembled. Stopped leaking but now the lag is back. Mech suggested fowled plugs so i put iridiums in today, no better

Any suggestions? And yeah, I would love to put flat slides on and what not but money is a serious issue.

Cheers yall.

[M.V.]

I'd start with carby setup, especially float heights & work from there, it's all free

Did you check float heights when it was all apart?

Whereabouts are you located mate?

[fung]

could also be crud in the taper of the float valves, or a fuel tap not delivering fuel only on demand, but leaking down if the diaphragm has failed.
A) clean carbs and blow out jets, galleries etc.
B) disconnect the fuel line and see if fuel still runs.
C) float levels.
And and and and
Cheers
Fung

[BigAl-TC]

The surging is the needle jets, aka emulsion tubes, wearing when the needles flutter in hole, causing oval holes. New needle jets required. I agree on the float heights being very critical as well.

[Stu99]

Remember to tune and test one change at a time. All the tuning circuits of your carbs have an effect on each other so changing more than one thing at a time can lead to a viscous circle of tuning.
Also have a look at Factory Pro's website. There is some very good information on tuning process there.

[jim280885]

OK, so here's the latest.

Bought some standard carbs without seized mixture screws and slapped them on. STILL have the flat spot... It is running rich (i gather from the popping on overrun) but pulls as strong as it did with the old ones on. Is having these ones balanced and mixture set likely to actually eliminate the flatspot? or am I barking up the wrong tree with carbs? Could it be TPS or something else? I have put new plugs in too, so am a bit lost as to what could be causing this sh!thouse lag.

Cheers gang.

[Con Rod]

popping on the overrun is not necessarily a symptom of rich running, could be lean too, and in any case a bit off popping on the overrun is quite possible from a good mixture.

There is no half measures on tuning carbs, they are either all right or all wrong. First step would be to set them to stock carb settings and tune from there.

this is a good giude
http://www.factorypro.com/tech_tuning_p ... gines.html

but you should do some research on the site with the search function on this forum

This thread is full of useful info
http://www.trx850.com/phpBB_forum/viewt ... kit#p74618

as is this

http://www.trx850.com/phpBB_forum/viewt ... =36&t=7983

With the TPS you can test it by following
1. Turn on ignition.
2. Disconnect TRP
3. Reconnect TPS
4 Observe Tacho.

If your tacho swings to 4000rpm your tps is set correctly

[jim280885]

To update;

Spent all day playing mix and match with carb bits. Found out one of the dynojet needles is bent, so am now running DJ emulsion tubes with stock needles. Floats set at 14mm, mixture screws set at 2 turns out. STILL have the flat spot. I am wondering now whether it could possibly be something beyond the carbs, but what? I have had 2 completely different sets of carbs on it, still there, then my mix and match set, still there. it MAY have been minutely better with the mix n match carbs, but this might have been me being optimistic/so fed up that i was feeding the throttle on far more aggressively

Also, for some reason the wee O ring in the TPS wouldnt seat properly, so i ditched it (the o ring) in frustration. I have had it on and off about 5 times now and never had this issue. I researched the tps mod but it looks fairly complex if the bike is going to run worse for having done it.

I have started just riding around the problem on the road but it goes against my sensibilities to accept that the the bike doesnt work as it should. grrrrrrrrrrrrr.

[Mincehead]

Hmmm, might be time to have the carbs ultrasonically cleaned to remove any remaining stubborn residues. it WILL be fuelling I`m almost certain of that.

[Mincehead]

Hmmm, might be time to have the carbs ultrasonically cleaned to remove any remaining stubborn residues. it WILL be fuelling I`m almost certain of that.

[bagmaker]

fuel? -don't bet on it

see here for an ongoing saga

http://www.trx850.com/phpBB_forum/viewt ... t=bagmaker

I still have the issue, now my culprits are down to:
ignition pick-up coil - i have checked it and it seems fine, within spec and clean -
plug caps - unlikely to allow clean running after 3500rpm and not before, unlikely to allow good idle
ignition wiring - somewhere in the spaghetti there is a gremlin.

EVERYTHING ELSE has been replaced.

My issue seems heat related but not directly engine heat, like heat soaking into the electrics. Its a horror to ride in the city but ok-even running hard-in the cool backroads, as long as there is ample airflow.

weirdest thing, lost all my hair looking for the problem.

[jim280885]

OK, finally on the right track I think... Yesterday I pulled the needles and put them up to the highest notch (they were on the middle notch) and it was terrible. So i put them on the lowest notch and ALSO wound out the mixture screws half a turn (to 2.5) and the flat spot is ALMOST gone!!

Tomorrow i'll open the screws another half turn and see if that irons it out completely... here's hoping. Much less popping on overrun now too... which is a bit shit.

[Con Rod]

check your float level

[zednine]

Im watching this thread with interest as I have exactly the same issue ........ Ive bought a set of carbs which I know run perfectly on a Trx ( I took them off my Trx and put them on a Tdm for a mate )
so Im keen to know if this is definitely carb related

Chris

[Killerwhale]

Im watching this thread with interest as I have exactly the same issue ........ Ive bought a set of carbs which I know run perfectly on a Trx ( I took them off my Trx and put them on a Tdm for a mate )
so Im keen to know if this is definitely carb related

Chris

Easy test is to wack the throttle from idle, if it goes to same idle fast it´s good...
If it hunts up hi before settling it´s lean....
If it dips under idle before going up again it´s rich...