Yet another cold start problem


XS400 Enthusiast
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Brighton, UK
Hi all,

I'm new here but not completely green. Back in the 80s I had two XS250SEs, then in 86 finally got an XS650SE that I had for 10 years and did loads of miles on, boy what a bike was that, really loved it and it served me so well... never should have sold it (GBP 650 in 1996, aaaargh ... and just after a rebore!).

Anyway, was out of biking for too long, recently moved, nice garage (!), decided it was time to get back to biking. Looked for another XS650 for a long while, lots of overpriced rubbish around, and got outbid on the 2 nice ones that came by. Then along comes this quite nice but non-running XS400SE locally for not too much money.. well I thought, time to try the 400.

The bike was advertised as 'used to start and run well last year but not used for a while and now won't start'. I did get it started before doing any work but it was a pig, took 30+ minutes of hard work on the kick and playing with choke and throttle. Eventually it started on 3/4 choke and blipped throttle. One started it ran really fine, even after a couple of minutes the choke could come off and it would settle to a very even, slow tickover!

I have since done a lot of cosmetic tidying up and replaced the rotten stock exhausts with Commando peashooter exhausts, with some baffling added, the story on that is over at ('Exhaust' topic, same handle), will copy it over here and add photos if anyone is interested.

Apart from that I did the totally easy obvious things - bled of all old fuel via carb float chamber bleeds (used clear tube, old fuel did look clean)... put in some new high octane, fitted new plugs, checked for presence of spark, checked rest of electrics are OK.

OK to cut to the chase the problem is it still has a tremendous disinclination to start. The symptoms are identical to when I got it. Putting the petrol tap on PRI a few minutes before attempting to start does not make any difference. It will only ever start with 'choke' [Enrichener] 3/4 on (it is a pull-out choke with two click-positions beyond zero, it has to be between click 1 and click 2, which is tricky, and even then it takes at least half an hour, during that time it will pop occasionally, (can smell unburnt fuel) then at some completely random time it will suddenly catch.

What seems odd to me is this: once only caught, it normally keeps going and in any case will very soon tick over absolutely fine. :wtf: Or if starting with a warm engine, it will start immediately / normally. Ambient temperature here is around 15C, I think that's about 60F? So it is cool, not cold. Once warmed for two minutes, choke can be right off, tickover is even, and power seems OK at least at lowish revs, ... it is not MOT'd yet so I haven't got room to get it up to any speed, but up and down the lane it seems to pull strongly and smoothly in 1st and 2nd up to around 30mph.

If the bike is then left even for 3 hours or so (only just back to ambient) then it is back to the whole 30-minute ritual to get it started again. My right leg will be way bigger than my left in no time!:yikes:

YES ... I have read the forums at length! :doh: Everything seems to point to dirty carbs... blocked (or at least varnished) pilot circuit? Although in that case the normal tickover so soon after the starting problem does seem odd, but maybe I have misunderstood something?

OK, I'll clean the carbs really really thoroughly (as well as the other obvious things that I am more confident to do right off the bat like the static timing, the valve clearances, maybe check coils and condensers etc) - BUT - before diving into something that seems a bit fiddly and with the potential to mess up (carbs), I though I'd ask to see if anyone has had experience of these specific symptoms before?

Cheers all.
Hi and welcome to the forum. Can I assume that your bike does not have an electric starter? If it did, perhaps you could try using a booster battery direct to the starter leaving the bike battery to do the sparking (I think xsLeo did a write up on it). That might save your leg while you are working on it.
It might have been Leo who also wrote about the cold-start jet getting fully or partially plugged and needing to be unplugged - sometimes with a really thin wire.
Anyhow, best of luck and keep us posted. And, speaking of posted, a pic or 2 might be nice.
Id say that a good, thorough carb cleaning Is in order. Tear them down, remove all rubber & plastic and soak the body's and all jets and metallic pieces for 12-24 hours. Take them out, blow out all the ports and pieces, run fine wire through all you jets and crevices. Clean THOROUGHLY! The previous owner probably put it up w/ gas in it. Remember, take pics before you disassemble and as you go so you can remember how to put them back together. Do it in an uncluttered, clean space so as not to lose anything. And be careful when you pull out your choke rod, don't wanna lose that lil spring & bb that will shoot out!
Yea it sounds like the choke (enrichener, you are correct) is not doing its job properly. I had very gunky carbs when I first got my XS and it would take me about 30 minutes to start it as well. It wouldn't run great then though, but after I cleaned the carbs for the third time and I got a new battery (that had died on me in the meantime, I do have an electric starter), all was well. Starts on first turnover ever since.

Only thing to be careful with is the jets in the carbs. they're brass jets, therefore quite soft and you can break them easily if you don't use the right sized screwdrivers to get them out. But if I can do it (I'm a bit of a bull in a china shop sometimes), so can you.

and I agree on the pictures :) good luck with getting the bike to run !
Thanks very much Lou, Bizzy and Willem!:thumbsup:

I have not taken any decent shots yet, just a quick snap outside the house, see below. It is coming along, over half way there now... As you can see I have kept it very stock except for the Norton Commando (...Triumph mount version) peashooter exhausts, plus a bigger Highway Hawk mirror on the right. Need a LH one to match now!

There is a story about those exhausts, once I got everything worked out they were a drop-on replacement, the hanger brackets didn't even have to be modded. A few little bits needed fabricating but only the welding of the tube reducers stumped me and had to be subbed out, everything else was done easily at home. If I had been able to buy the Maremont (possibly #548520??) tube reducer available in the USA (but sadly it seems not over here) and had known all the info, it could have been done in an afternoon. I have plenty of photos, and at some point - probably next winter - I plan to post the details here.

Once the engine is running well (and compression does feel pretty good on the kick, so I'm hopeful it is a good engine at heart...), then it is MOT time and a quick final tidy up for summer with polishing where sensible, and replacing loose & missing rubber grommets etc. I sold my XS650SE about 17 years ago and am absolutely itching to get back on two wheels.

The chrome on the rear fender, handlebars, and carb covers is all pretty nackered so those will come off for re-chroming next winter, if I get that far then it should end up a really tasty bike for a reasonable outlay.

Hope to post a proper set of photos, & youtube for the exhaust note, as soon as it is on the road. :bike:


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There is lot's of info on cleaning carb's in the forum but here is the 2 thing's that made a huge difference for me during my second carb clean.

In the attached pic...

1) There are spring's inside the float needles. Mine were completely seized (missed this on the first clean). You can GENTLEY work them free using carb cleaner and needle nose plier's. This took me about 1/2hr.

2) There is a VERY small passage way in the float bowl (where the red thing is). This will effect the choke BIG TIME and again totally missed on the first clean. It took me about 1 hr for each bole to clear using very small needle's and carb cleaner. There maybe something better than the needles but what ever you use DONOT break it off inside the passage way.

Id also make sure that your tank is reasonable clean, internal fuel filter is clean and you have a 2nd fuel filter between the tank and carb

The other pic is of my bike. Got new header's and pipe's on the way

Hope this helps


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... The other pic is of my bike. Got new header's and pipe's on the way ...
Nice looking bike - especially the seat. Did you re-do yourself or inherit it that way?

Also, how did you make out with the misfire on one side - was it the coil in the end?
Early this spring, before I got the new battery, my Maxim would sometimes start on one cylinder (first start) on a cold day. After a few seconds I could rev it and the 2nd cyl. would kick in and it would be fine for the rest of the day. Since getting the new battery it has never happened again.
Nice looking bike - especially the seat. Did you re-do yourself or inherit it that way?

Also, how did you make out with the misfire on one side - was it the coil in the end?
Early this spring, before I got the new battery, my Maxim would sometimes start on one cylinder (first start) on a cold day. After a few seconds I could rev it and the 2nd cyl. would kick in and it would be fine for the rest of the day. Since getting the new battery it has never happened again.

Hey Man...

Except for the handle bar's, the bike is pretty much they way I got it from the PO except for the green mold which everything in the pacific northwest seems to get when they sit for any period of time.

I'm a huge fan of Maxima line of product and I use there SC1 clear coat spray on my dirtbike's so tried on the xs400!!!!

One of the pickup coils's was bad. Once I replaced them and cleaned the carb's the second time, she start right up!
Hi filterx,

Thanks for the carb clean tips. I have bought a load of distilled vinegar and hope to do the clean this weekend.

Last weekend I did the valve clearances (all fine), points gaps (fine) and timing (one side was a bit out). It already starts a fair bit easier, which is kind of interesting...

Last weekend I did what I thought was a very thorough carb clean, it took 5 to 6 hours all told... and I'm still having the same problem! No real change at all. AAARRGGGHH!:banghead:

After this experience plus more VERY extensive reading in the forums, there are a few things I can pull together here that may help others with the same problems. Thanks to all those who have posted before, especially BCWare for the carb clean videos ( good to record with a better camera one day!).

1./ CARB CLEAN. Probably the best carb clean guide is here:

This is a big old 72 page PDF! :) All big clear photos and goes through lots of detail. NB this is for Suzis, so be careful about any bike-specific info such as float heights that might be different! ...

2./ ... Oh yes, FLOAT HEIGHTS:
The Haynes manual does seem to be wrong / misleading at least for some SOHC XS400 models :yikes: (it gives a single float height of 32mm for XS400). I think the other , 'Short' service manual available on this forum i.e. here:

View attachment 3882

has more complete data for the various different XS400 models. Float heights can be found under 'Tune-Up Specifications' on page 1272. For most models the correct height seems to be around 22mm or 26mm.

In any case the best way to check is measure the fuel height using a clear fuel line connected to the drain hole on the float bowl... open the drain cock, and IIRC, the fuel level in the line (when held up of course) should be about 2mm below the carb body / float bowl junction with the carb horizontal and right way up. Probably best to do out of the bike, maybe hold carb gently in a vice or similar.

3./ Going back to CARB CLEAN - Some pitfalls.
The main pitfall seems to be not doing it thoroughly enough. You really have to do it ridiculously thoroughly!!
-There is a passage in the bowls and also a small bore sticking-up tube in the carb bodies, that get fuel to the Enrichener and Pilot circuits. These have to be specifically cleaned out and even a 30 minute vinegar boil may well not do the job on its own. They need careful poking through with wire (in general, use soft wire [copper or brass] and / or be very careful), then flushing through with lots of carb cleaner. Make sure the carb cleaner squirts through and out the other end in all cases! Check for side openings in all tubes and clear out as needed.

All of this very thorough cleaning also applies to the more obvious carb parts like main jet, pilot jet, emulsion tube, float seat, and the 3 (or more?) little holes in the venturi.

4./ Be aware that the bike can start and even idle quite steadily on the MAIN JET. I hadn't realised this before careful reading. (duh). I think the throttle stop (knurled knob underneath and between carbs) had been adjusted on my bike so that it idles off the main jet circuit. Important implication - a steady idle does NOT necessarily imply that the starter and / or enrichener circuits are unblocked!

5./ Starting technique. Some have mentioned that opening the throttle while starting will hinder the operation of the enrichener / 'choke', if I understood correctly by 'diverting' vacuum which would otherwise draw air (and fuel) through the enrichener. This does NOT tally with my own experience so far ... my bike only starts with use of the throttle. However, remember my bike still isn't starting right, and 4./ above is probably how my XS idles. So it is very possible that this comment about not opening or even blipping the throttle is quite right for correctly fucntioning carbs. On mine, as of now it needs 2/3 'choke'; two kicks with throttle fully open, a kick with throttle fully closed, and finally a kick with throttle blipped a little, at which point there is a very small chance it may cough or even start! It is fiddly but I'm getting better at it, used to take half an hour now it only takes 20 minutes :D

6./ More carb clean. Got talking to a helpful local bike dealer. He said try using coke. (I guess diet coke as you don't want sticky sugar residue!). This is not as stupid as it sounds. Coke really cleans metals to a bright finish, I have used it before for cleaning copper items for high power radio use and it really does the business for that! It would probably be best as a final polishing clean after the boiling... Boiling in pure distilled vinegar did leave a silver powdery deposit on parts of my carbs (I think it was Mazite from the bodies dissolved and then deposited onto the steel parts i.e. the throttle linkage etc), and the vinegar also discoloured the brass butterfly valves of the throttle.

All this is just for now as a temporary update. I'm keeping at it, and hope post back more usefully later when it is completely solved... I really hope so coz starting like this is not much fun. :banghead:
*PS* as mentioned on another thread, I did a slightly longer test ride this time... once running, power is amazing. Virtually wheelies in second gear, screams up to the red line in 2, 3, 4 gear in what seems like very little time and with no noticeable flat spots. There really does not seem to be any problem at all once started!!

Filterx, I did clean out & check the bowl passage, float needles & springs were fine, etc. Fitted brand new inlet stubs on re-fitting carbs this time (& cap is on unused vacuum tap!).

My carbs looked very clean all through. Found almost no evidence of varnish anywhere. Some black flecks in the vineagr after boiling. Will post some pics later.

In the time in between I'd also: charged battery, checked coils, new condenser. Before that I did points gap, static timing, valve clearances cold.

My XS has got electric start but most of the time I feel its better to use the kick - to save stressing the battery and starter motor, and to eliminate low-voltage as a possible cause. I have tried the electric start, it normally will crank OK and once or twice it has even started on that, so it does not seem likely that low volts at the points is a factor.

If anyone has any bright ideas, *please* chip in! Else it's carbs off again at the next opportunity and a happy, happy girlfirend! :doh: :laugh:
Hi Scorpio,

Thanks for the input.

Have not changed anything from stock, as yet:

The air filter & air box are 100% stock. OK, I have replaced the Yam exhaust with the straight-through Norton peashooters. HOWEVER the peashooters are packed out with lots of fine wire wool followed by chicken mesh to reduce noise. I don't think this should change airflow enough to require re-jetting - although yes, it may be required.

In any case, should the main jet really affect starting? I thought the main jet was only supposed to kick in at higher revs / higher throttle openings? Shouldn't it be the pilot jet to change for starting and low power?

One thing I did not do yet is fiddle with the mixture screw. As found they were 4 turns out, on the rebuild I went for 3.5 turns out. I'm going to have another go at the problem now and after trying a few different starting techniques the first thing I will try is fiddling with the mixture screws. Further out (anticlockwise/ leftwards) is richer, right?

If this fails I plan to try another carb clean with emphasis on passages in the bodies and the little copper tube that sticks out.
Waaaaaaahey! My bike starts fine now!:thumbsup: :D That should be the end of this thread, except maybe I will post back details of any jetting changes, if they seem to be necessary once the bike has been run properly.

Went out this morning and tried starting without touching the throttle at all. Put on PRI a few minutes before. Second kick got a burble, then after 3 or 4 kicks it started fine! :thumbsup:

Not sure if this was some water /muck left after the carb boil stopping it from working last time, which got blasted and heated out in my test run then. Or maybe it's the proper starting technique, or maybe even both who knows...

Anyway for those having trouble with starting and cold starting, not touching the throttle at all during starting - and until it has been started for 60 to 90 seconds - is another worthwhile thing to test out. And bear in mind after carb boil it might take quite a while for residual vinegar / water to be completely gone.
To answer part of your question on Jetting,Our bikes have idle jets on the side of our venturi.The mains aafect the flow of gas into the carb,If you increase the size you have more fuel which increases power and easier starting.When I had my carbs in tune I very seldom had to use the choke to start it.The only thing that kept it from starting was still having my suummer oil duriing cld weather.As for the pilot jet You may know more about how it works than I do Im not realy sure how it works or what it does.
Anyhow Im glad you got your bike running again.Im going to work on that this weekend with my bike.