poor running at low revs, engine stuttering.

[danbaldyman]

I have owned my 98 trx for 5 years now. Has never had any problems until recently. I have been using it at least once every two weeks all through the winter, and on one particularly cold day it was spluttering and stalling. On my return journey when the weather wasn't so cold i gave it a reasonably good thrashing and it appeared to work fine. Since then it has been very temperamental. So i drained the tank, stripped and cleaned the fuel tap, stripped and cleaned the fuel pump cleaned and blew through all pipes and cleaned the air filter. Put it all back together, still having troubles. The most prominent/noticable thing that seems to be something that could potentially point to the problem. When on the side stand, and running every now and again, perhaps one every 30-45 seconds the bike stutters. And i have noticed also that when this stutter happens there is a pulse on the vacuum pipe. My vacuum pipe( not sure if this is the same on all trx's) has two seperate pieces, with a joint section linked with a smaller diameter pipe sleeved in between the two adjoining sections. And when the bike stutters the pulse is seen here, the pipes part slightly and then move back together. Hope this is making some sense. So my next thougths are. A does this vacuum pipe set up seem to be correct? B my first thought was to change this pipe for a one piece section from pump to carbs. Or C, am i barking up the wrong tree all together and is my bike showing similar symptoms to that of someone else on the forum? Your ideas and experience on this matter would be most welcome. Thanks dan

[Mincehead]

You don`t mention cleaning the carbs, have you had the carbs off the bike or drained the float bowls? There may be some moisture or crud in the float bowls. I think the vacuum hose movement you`re seeing is simply a vacuum pulse caused by the stutter in running.

[danbaldyman]

So would you say that the vacuum pipe pulse i am seeing is a natural thing? And as mentioned in my first post is the vacuum pipe supposed to be made in two sections with a link piece between, are all trxs like this? Or has this been a quick repair job from a previous owner? I haven't removed the carbs or cleaned out the float bowls yet as i thought it best to get information from the guys in the know on this forum before doing so.

[dicky]

There are two vacuum pipes, one from each inlet manifold.
One connects to the the fuel tap, the other to the fuel pump.
The standard fuel tap can be run without vacuum if you put it in the PRI position, but you do need to block the port on the inlet manifold.
It may be worth checking that the carb water circuit, which is actually a heater, is still connected. In Godzone we don't get many days when the temp is cold enough to need such a thing, but if you're in Blighty then you probably should have it all connected.
This is a hot water circuit that feeds through the carbs from the hoses either side of the thermostat.

[danbaldyman]

I have just checked my current set up from dickys post. As it stands my bike has the 2 vacuum pipes. Both running from the inlet manifold, one to the fuel tap and one to the fuel pump. Also both pipes are present running to the carbs from the hoses attached to the thermostat housing. I have also checked coolant levels which are within the required limit. Any other ideas? When i next get time i hope to remove the carbs and check the float bowls, but with my bike not being kept in a garage and therefore in a situation where i need to do and complete the job in one session i would prefer to explore all other potential problems before doing so. I think i will change the pipe with the joint section as mentioned in previous posts to a one piece. (unless someone out there knows of a reason why they are meant to be in 2 sections) As the joining piece holding them together has hardened somewhat and yellowed. And could possibly not doing its job properly. Thanks dicky and mincehead for advice so far. Any other thougthts on the matter would be welcomed. thanks dan.

[Mincehead]

It certainly won`t do any harm to replace that hose but I still believe it`ll be carb issues, water and or crud in them being most likely, oxidisation in air drillings is possible too.