I had hoped to have my 79 V50 completed this weekend. It was running recently but I had concerns over the front brake and decided to fit a 13mm master cylinder to hopefully improve matters - at the same time I also swapped handlebars for some which gave me a more upright ride. So far so good - I was able to ride the bike but noticed that I hadn’t routed the throttle cables very well and wanted to correct this. And this is where my troubles no doubt originated! I didn’t fancy removing the twistgrip and re routing the cables that way as I’d had enough issues getting it, along with the attached switch to grip the handlebar so instead I removed the carb tops, disconnected the cables at that end then routed them where I wanted them to be and put everything back whence they came - or possibly not!
The bike will now start on full choke when cold and run after a fashion for a minute or two but then shows signs of running rich (black smoke) then it starts to chug and eventually stops and won’t restart until its cold again. Apart from taking the carb tops off I haven’t fiddled with anything else but can’t see what I might have done wrong - any ideas or solutions most welcome!
It sounds like you’ve fouled the choke cables and they are preventing the choke plungers from dropping fully home. By ‘fouled’ it could be as little as having pulled the cable out of the choke housing on the carb and its now sitting on the top of the cable adjuster.
As regards the handlebar switch: assuming that they are the handful of dolly mixtures type, the way to secure them to the bars is to use the two long screws to close up the two halves and nothing more, then use the small grub screw to prevent the shell from rotating. If you try to use the long screws to clamp the switch to the bars, you will eventually strip the threads.
Yep, as Dai says, it’s almost certainly a case of inadvertent full-choke. Make sure the cables are slack enough to allow the choke plungers to seat fully. It’s probably just the cable tension that’s causing the problem, but the plungers can stick in the housing if it’s gummed up; or if the spring has lost its oomph; or if the little rubber seal/washer at the end of the choke piston has deteriorated. The good news is that it’s an easy and inexpensive thing to fix
Many thanks for your responses - I suppose it was obvious that the choke was the culprit though I was sure I hadn’t fiddled with it. I found that the right side choke cable was curved quite sharply so I attended to that and satisfied that the cables had some slack when the choke not in use.
I ran the bike but all is not well! I noticed that the right cylinder was quite cold after running for a minute or two whilst the left was hot. So it had been running on one! This is not the first time this has happened. On one of my first trips out on it, after covering about 35 miles the bike went onto one cylinder. It chugged along for a few minutes then suddenly returned to normal for a few more miles then repeated the performance. I did read somewhere that one of the coils could pack up if they got hot and this was a day about a month ago when it was pleasantly warm. I’ve been on a couple of shorts runs since without issue - not that one anyway - but today the bike was parked in the sunshine. My machine is a 79 model V50 with Bosch electronic ignition and I’m at a loss as to what to do next. I’m in the South East and wonder if there’s a Moto Guzzi equivalent to the Boxer Guru, Jim Cray , somewhere I can call on.
Right. Pull the connector off the r/h igniter unit and check for corrosion. I had one with exactly that fault waybackwhen and the l/h igniter unit turned out to have green connectors. Some contact cleaner fixed that. Secondly, if my 67-year-old brain still has a correctly operating recall mode, the Nippon coils garnered a bad reputation for allowing water ingress into the HT lead exit which led to intermittant breakdown.
IF the problem turns out to be a coil, you don’t need to buy a replacement Guzzi one. All you need is a coil (or coils) from any Japanese bike that have the same resistance measurements. Igniter units turn up all the time on ebay (Ducati, Laverda, Guzzi) - just double-check the part number to be sure you get one with the correct advance curve.
I took one apart once, just for interest. There’s practically nothing in the box - an RC circuit to provide the advance curve and a big fat transistor to fire the spark, plus a couple of components to keep the circuit stable.
Guzzi coil “Ohmage” is not too odd, plenty of modern cheap coils with same parameters. Just buy two new ones and keep old as a reference. I know coz I went other way, and found Yamaha YBR250 accepts old Guzzi coil with no fuss!
Many thanks for your responses - I suppose it was obvious that the choke was the culprit though I was sure I hadn’t fiddled with it. I found that the right side choke cable was curved quite sharply so I attended to that and satisfied that the cables had some slack when the choke not in use.
I ran the bike but all is not well! I noticed that the right cylinder was quite cold after running for a minute or two whilst the left was hot. So it had been running on one! This is not the first time this has happened. On one of my first trips out on it, after covering about 35 miles the bike went onto one cylinder. It chugged along for a few minutes then suddenly returned to normal for a few more miles then repeated the performance. I did read somewhere that one of the coils could pack up if they got hot and this was a day about a month ago when it was pleasantly warm. I’ve been on a couple of shorts runs since without issue - not that one anyway - but today the bike was parked in the sunshine. My machine is a 79 model V50 with Bosch electronic ignition
You could try swapping the coils over to see if the misfire changes sides. If not, it’s likely dirt in the offending carb that’s causing the misfire. My V50 does this occasionally, usually after her winter lay-up. A good clean out sorts the problem.
This Bike is proving to be a steep learning curve! On Daigs advice I thought I would have a look at the igniter units and eventually found out how to get at them partly thanks to the P/O who had put the alternator rotor removal tool in the box of donated odds and sods that came with the bike. However I’m stuck at the “pull off the connector” stage as I presume the black plastic plug comes appart if you know where to squeeze! But I don’t and I’m assuming that the igniter unit doesn’t have to come off first. I’m also a bit confused with markings made by same P/O.
I noticed when I first had the tank off to investigate that the top and newish looking coil had a white “L” painted on it which I presumed to be the left cylinder and the one working OK. The coil below it looks to be in a sorry state so I won’t be surprised if it turns out to be the villain of the piece. What doesn’t add up though is that he has also put a small “L” on the igniter which is at 10 O’clock when facing to the rear of the machine! My Workshop manual clear shows the igniter in this position fires the offside cylinder.
No, no, no. Those are the ignition pickups behind the shield behind the alternator. The ignitor units are attached to the sides of the mudguard behind the sidepanels. It’s a six-pin connector block with 6.3mm (1/4") female spade terminals in them.
As you’ve got that far into the front of the engine, just because you’re there and no other reason, check the length of the alternator brushes vs the acceptable length noted in the manual.
Phew who knows what damage I might have inflicted had I carried on. Its all back together now but not running . I’ve been busy with my other bike - an Enfield Hunter 350 which toppled over on me and bent the gear lever.
But back to my V50 - I thought I’d sent a response to DaiG but can’t see it. I was asked to give it a title but can’ see anything else from me.
As I’m satisfied that the Igniters are clean and the bike cuts out on the right cylinder I’m inclined to suspect the coil which is an original item. The other coil looks fairly new but is a different one.
A new coil is available from Stein-Dinse at a good price and their postal service is second to none. Don’t forget to ask for your 8% discount as a member of MGCGB:
"phew thank goodness for this Forum and its knowledgeable contributors. Who knows what catastrophe I might have started without DaiG!
I did check the brushes which look as if they are fairly new as there’s plenty of life still to go!
Similarly I’ve found the two Bosch triggers - the contacts look clean but I’ll give them a squirt of cleaner tomorrow before exploring the coils a little further,
I seem to have lost a response from Mandello Tractor ref swapping bits around"
“Nah I made an assumption which I should not have done and that was to assume that you understood what I meant by ‘igniters’ and knew where they were mounted, or (again, an assumption) that you knew to check the manual. I appreciate the message but that one’s on me.”
A new coil turned up on Tuesday and its exactly like the one already installed and working on the left cylinder so I was able to copy the wiring and connect them correctly.
So confident that all should be working fine I finished the job, popped the tank back on and …it refuses to start! There’s a fat spark on both sides but no attempt to start with or without the ‘choke’.
Unless someone can suggest an alternative I’m proposing to take off the carbs, clean them out , replace the seals and gaskets and reset them following one of the You Tube tutorials or the one linked to the Gutsibits website.
I won’t be starting for a few days as I’m away on my other bike lest I forget what went where in particular dismantling and refitting the air filter!
Footnote to my previous item, I have fiddled about with the carbs trying to sort it out but I have made things worse! The bike was running OK when I got it apart from the tendency to run on one pot!
Just remembered something - I presume these are VHB carbs? Assuming carbs are 100% healthy, using the enricher (‘choke’) in summer tends to be too rich and it won’t start - guess how I know - my last MG with VHB’s I replaced all the jets because they were partially blocked. One thing this did was allow the mixture screws to return to the standard 1.5 turns out. Hitherto they had to be 2.5 turns. The other thing that happened it flooded on ‘choke’ and wouldn’t start at all, first time after fitting the new jets. Needed grinding on the starter at WOT to clear it out, ‘choke’ off, then it had a chance of going. Then I remembered, starting my Spada (same carbs) in summer only needed a couple of twists of the twistgrip to pump a bit of petrol up, and the enricher must never be used except when weather is really cold, like in the depths of winter.
Bad luck Eddie. Everything you have written so far points unambiguously to a carburettor issue, as I originally suspected.
Take them off, dismantle completely – noting the number of turns out from fully closed for both the mixture screw and the throttle stop – then soak all the bits in carb cleaner. Agitate with an old toothbrush to remove stubborn deposits and run a fine wire – a straightened-out strand of old clutch cable is ideal – through the jets. Blow everything out with compressed air. Check the float heights. Then put them all back together with new gaskets and o-rings, all available from Eurocarb, and set mixture screw per the manual, throttle stop screw per the measured number of turns on dismantling.
You will solve this problem. It’s only a carburettor, not rocket science. There are only a limited number of possibilities. Let us know how you get on.
I made an assumption which I should not have done and that was to assume that you understood what I meant by ‘igniters’ and knew where they were mounted, or (again, an assumption) that you knew to check the manual. I appreciate the message but that one’s on me.”