Yamaha SRX600 - minor problem

[srx ijk]

Hi All - my SRX is finally running pretty well - using E5 petrol it starts easily, ticks over steadily and pulls well. However when in a low gear around town, with throttle just off tickover there's some very slight but irritating hesitation/hunting. Not a huge problem, as when accelerating firmly it's not noticeable.  Bike is standard, no air leaks, new float valve and seat, new coil and lead.
Any thoughts on carburation adjustment - too rich?
Thanks!

[iansoady]

Is it a slide carb or CV? I've found with Amals that the recommended slide is often a bit on the weak side and going up a size helps. It's the slide that governs the transition from idle but you can sometimes get round it by adjusting idle screw / needle position.

[srx ijk]

Hi Ian - SRXs are fitted with an (in)famous twin carb - CV and slide; slide for lower speeds, the other CV side for higher speed.

[themoudie]

Aye srx ijk, welcome to the madhouse!!

May I ask if your machine is the twin shock or the mono and what year and CC's?

My first thoughts are, have you renewed/cleaned the air filter? And, what colour is the plug?

Ian's AMAL carb advice could apply, as it is the slide carb part of the instrument that is controlling the engine running up to half throttle, when the CV side starts to take over.

I have both a twin shock 1986 1JK 600 and a 1991 SRX 400, with a 1991 XT600E motor installed and both are using the standard slide/CV carb.

Also check that your choke plunger mechanism is not seized and the little rubber seal in the end of the choke plunger is in good condition, or else you will get bottom end fuelling problems, as you describe.

It's part #46 in this fiche image of the carbie on the Fowlers (Bristol) website. Link: SRX600-1xl-1987-999-a/carburetor
The price is pretty eyewatering! 

So try NRP-carbs, they supply spares in good quality viton that withstands the E5 and E10 fuels Link: NRP-carbs

Whilst you are under the tank check all of the fuel hoses for cracking perishing as either E5 or E10 will destroy non-VITON  fuel pipes and if they leak it's going to be all over a hot engine, with no way of getting to the fuel tap on the underside of the tank!    I was lucky and found that mine had perished, so was able to replace them, without incident. However, I had a small grain of muck hold the float needle open after a 60 mile canter up the A9. When I stopped at some temporary traffic lights the carb overflowed onto the running engine and the hot exhaust and the bike and I were enveloped in petrol vapour! Luckily, the vapour didn't ignite and turning the engine 'OFF' shut the vacuum fuel tap and stopped the flow of fuel. It could have been different if I had left the fuel tap in the 'PRIME' position. 

Do you have a workshop manual for the machine? If not, please PM me, with your email address and I can forward you a *.pdf file of the manual.

I hope that this helps you find the gremlin and SteveL, SteveH and IanR may all chip in with their pennysworth. 

Good health, Bill

[srx ijk]

Thanks Bill for your very full response!
It is a twin shock model with a relatively new/clean air filter.
I will check the plug - it hasn't been out for a while.
I had the carbs apart last month and the choke plunger was intact and seemed to be working fine, but I will double-check.
All the under tank hoses have just been renewed with e10 resistant rubber (I had minor petrol dripping which I thought was due to a defective hose but turned out to be a dodgy outlet spigot on the undertank valve! - fixed with metal mix araldite)
Glad you didn't combust on the A9 - fyi I've had similar flooding issues, with engine turn off being the only way to stop the flow, hence the new float valve.
Thanks - I have the manual.
The hesitation when just off tick over wasn't so obvious in the past so it probably results from something I've not put back properly - or else I'm just being over-sensitive about it and probably wouldn't notice if I lived somewhere other than congested north London!
Anyway will check the items you've mentioned and update on outcome.
Glyn

[themoudie]

Aye Glyn,

My pleasure.

Another wee dodge that I found cleaned up the bottom end, was to use an NGK Iridium plug:

SRX600, 86?89, Standard: DPR7EA-9, Part #5129, Iridium: DPR7EIX-9, Part #7803, Plug gap (mm) 0.9

Taken from NGK parts finder 2022-23: Link: NGK parts finder 2022-23

You may have seen posts on this forum from andy230, he too has a penchant for SRX/MZ, with the 600/660 engine and lives, I believe, in the same area of "The Smoke". So, he may drop by on this thread.

Good health, Bill

[srx ijk]

thanks Bill - I was running an iridium plug but on standard at the moment. Perhaps will stick the pricey one back in to see if it makes a difference.

[Ian]

Hi there, I have read with interest this topic. Just a small note, if you change the plug try and blow all the crap out as the plug sits in a hollow that tends to collect all the road crap that is thrown up and falls into the cylinder when you remove the plug.  Hope you get/have got your fuelling problem sorted.
Ian

[Steve Lake]

thats a good tip ian, i'm lucky enough to have a compressor, so wheel it out to blow the cr4p away, of which there is loads usually, apart from the issue of all the cr4p falling into the cylinder there is the problem of the plug not seating properly when you re-install it.

[srx ijk]

Thanks Steve/Ian - good point, I've always been a bit wary when about road grit etc getting in when removing the plug, unfortunately no access to compressed air, so bicycle pump will have to do! Have fitted a diy fenda extenda so hopefully might not be too bad.
Glyn

[andy230]

Hello,

Previously in the dim and distant I have had the stator (inside the engine cover) start to break down, causing a misfire when hot (test the values at the multiplug, as per the book), and the inlet rubbers persihing to let in an air leak.

Maybe an air leak due to the little spigot (operates the vacuum tap on the SRX)?

Yep, choke is always good to check too.

Good luck!

a

 

[Steve H]

Have you adjusted the idle mixture ?. Also what rev's and gear is this occurring at, the SRX tends to hunt/surge at lows revs in 5th gear ?

[srx ijk]

Thanks Steve/Andy - the plug came out pretty black/sooty!
Have now put back an iridium one and will check later.
During one of my many carb removals I did adjust the pilot screw to workshop spec 2.5 turns out - on purchase a few years ago, it was less. So will screw in - looks a bit tricky with carbs mounted but will try with a short screwdriver.
The hesitation happens in second or third gear at speeds of about 20 to 30 mph
Glyn