My ‘carburation’ problem is now resolved, so it’s now Feedback Time.
I tried everything that I could think of to address the ‘sooty’ r/h spark plug, to no avail. So, I capitulated and gave it to a man who is wiser in The Way of the Spanner than me.
It turns out that there were various things that contributed to the problem:
l/h inlet port was leaking due to a dodgy thread. This resulted in very lean running on that pot.
The main culprit appears to have been the Dynatek electronic ignition was failing on one side, but intermittently. It chose one of the test rides whilst it was with the mechanic to fail completely on one side. One of the circuits on the back plate has gone south. At least it had the common decency to do it; A) while with the mechanic and, B) within striking distance of his garage.
Points re-installed and it runs like a top. A few other bits were also sorted that would never have been identified by me, so I am like a dog with 2 tails.
Now that it’s running properly, I’ve put a VERY nice V7 850 Special on the Marketplace …
VHB 30 Dellorto carbs. In 2015 I rebuilt my V1000 carbs as the bike was new to me and the carbs leaking.
The bike ran okay, there’s a Rita ignition fitted.
2024,2 months ago when undertaking a service, I found the threads on the spark plug hole to have partially stripped.
Cue a top end refresh. Timesert spark plug hole repair, New rings, gapped, honed bores, triple angle valve seats, valves refaced, mating surfaces lightly skimmed.
Put the lot back together. Ran the engine and found the right hand plug sooty.
Noted that when looking down into the carb with the top and slide removed a puddle of petrol in the carb body.
Cue another carb rebuild, noting that the o rings had gone hard and crumbly and the black conical tip of the needle valve was the same. (Ethanol joy?)
Bought Dellorto repair kit and viton NVs from Eurocarb.
Read the yellow Guzzi Manual and with 10g floats,Reset them to 24mm.
Bike runs, but bogs down when any more than half throttle applied.
Pulling choke on when running and fully opening throttle it goes better.
With the floats set at 24mm it means there’s less fuel in the reservoir.
I’m going to reset to the 18mm as recommended in Haynes to see if that rectifies the lean running
condition.
The yellow MG manual shows the VHB carb diagram with the nylon liner the wrong way round btw. So I’m not entirely confident with that now.
Took Carbs off yesterday. It’s impossible to adjust floats to 18 mm without bending float tabs to an impossibly acute angle. So rechecked levels to 24mm. Reassembled and found same bogging down at more than half throttle.
Plugs ( new NGK 6’s gapped to .6 mm ) show a light tan colour. Now wondering if the new standard air filter is restrive?
Can’t understand poor running condition.
Any ideas?
Float levels should be 23.5 - 24.5
Settings for V1000 are same as posted by Nik Wallace above.
If sooty I would check choke plungers are sealing properly - either the cables snagging of too tight or if the rubber pads and seats not sealing.
Last post says plugs are tan which sounds zbout right. I would recheck timing and carb balance.
Standard filter works, although can get clogged after high mileage because most of the air only goes through a small area at front of filter.
Thanks for replying, I replaced the paper air filter as part of the service. Last one was a few years old with less than 5000 miles on it. They are a really tight fit, and I thought I was assembling it incorrectly. I hadnt thought to replace the choke plungers, will do so, given that the rest of the rubber fittings have deteriorated.
Will recheck the balance with my manometer, I had used a carbtune, which arent a patch on the old mercury ones.
I had an older Morgan carbtune, same principal but I found it wasnt really working so I bought a couple of guages of Amazon and had much better results. I used the carbtune hoses with the restrictor 100mm from carb rather than the poor taps that came with. Its worth checking that the two dials are synced. I think I did it with a splitter ie 1 carb to 2 dials. I didnt need to adjust but theres plenty of stuff on the web on how to do it.
Prokomon Motorcycle Carb… https://www.amazon.co.uk/dp/B0BCP9SGZX?ref=ppx_pop_mob_ap_share
Ps Youve had the head off. Dont know how many miles youve done but might be an idea to retorque heads and reset tappets. You’re never at a loss for something to do when you have a Guzzi
Further to my post of 23rd May I’ve now done some more miles on my T3 with G5 engine fitted.
Bike is still running reasonably well but does seem to be a bit thirsty. Plugs are still showing a slightly rich mixture. Also, a flat spot around 1/8th to 1/4 throttle opening.
I’ve just fitted 60 slides (originals were 40’s) with the needles on the middle position. This is another significant improvement to add to the list in my last post. Just been on my usual test ride of about 25 miles. Bike will now go down to 20mph in top gear and pull off smoothly. No flat spots. Smooth transition through the throttle opening.
Plugs are now a uniform chocolate brown on one cylinder and slightly leaner on the other. I finished off by balancing the carbs with my Carb Tune U shaped manometer.
Bike ticks over nicely and responds to the throttle well. I need to take it for another test ride but I’m confident I’ve fixed it.
I hope this is of interest to anyone experiencing similar problems.
Recently I’ve read some posts on float height and adjustment. My floats are of the correct height 24 mm but are lighter in weight. They are the white ones. According to the Dellorto tuning manual this has the effect of lowering the fuel level in the float chamber.
I was not aware that the were different sized slides available for the VHB30s. Can I ask what the difference is between 60s and 40s and where you sourced them from please?
My Spada is pretty unmolested and the slides are marked 7545-40, it has black floats. The carbs have been cleaned occasionally, but nothing change from factory spec. I’m running K&N type cone filters. Personally I am a great believer that Guzzi knew how to set up these carbs and haven’t seen a need to change things.
Re: VHBT 30 carbs.
I got my 60 slides from Gussibits second hand. The slide cut away’s are in 1mm increments. My original slides were 40 so I’ve gone 2mm bigger on the cutaway therefore weakening the mixture at 1/8th to 1/4 throttle opening.
Eurocarbs have new 50 slides but they are expensive. On my existing 40’s I was going to start filing down the shorter side of the slides in 1mm increments to see what happens. I knew that If I messed up I could buy new slides from Eurocarbs.
Don-Spada raised a good point in that Guzzi knew how to set the carbs up. I think a lot of owners seem to be fiddling about too much with there carbs in response to worries about using modern fuel.
I think the VHBT carbs are a very good carb but it’s important to understand how they work. The tiny holes behind the atomiser are linked to the idle fuel circuit and must be clear of obstructions. I cleaned mine with an 016" guitar string. These tiny holes can easily become blocked when the fuel evaporates away leaving nasty gunge behind.
I bought the “Dellorto Tuning Guide 1.1” from Eurocarbs. About 12 quid. Excellent colour diagrams showing the flow of fuel and air at different throttle openings. I learnt a lot !
Sooty spark plugs can be an indicator that you are using a spark plug that is too “cold”.
Modern fuels burn cooler than fuels of the 1970’s, when our bikes were made. This means burn temperature inside of the combustion chamber is cooler. The spark plug has to be matched to this heat range.
My bike was fitted with standard plugs NGK BP6ES. I changed to a hotter plug. NGK BP5ES. It made a difference. With NGK plugs the lower the number the hotter the plug and vice versa. Other manufacturers have different numbering systems.
If the plug is too “hot” it can encourage pinking.
Too “cold” can cause sooting and fouling. This was my case. A new set of 6’s only lasted 300 miles before completely fouling with an erratic spark. Plenty of popping and banging etc. Not helped by the lead replacement additive in the fuel.
Be aware that if you see an R in the spec of your NGK plug. This means it has a resister fitted. In this case use a plug cap without a resister. Apparrently some electronic ignition systems are sensitive to electrical interference so resistors are necessary. Not a problem if you have a traditional contact breaker.
Update on odd runing.
Replaced the brass plungers in carbs as the ones from 2016 as rubber bits have gone hard and distorted. Checked that cables are not pulling them open.
Valve clearances were set after torquing down the head.
Found that adjusting pilot screw now had more effect.
Balanced carbs at idle and with throttle open halfway ( scary on a Convert).
Took bike for a ride. Engine began bogging down at opening throttle as before.
Then started running poorly, heart in mouth nursing bike back home.
Felt like running on one cylinder. Pulled N/S plug lead off bike died. Restarted then pulled O/S plug lead, bike carried on running.
Removed plugs, N/S plug colour absolutely perfect tan colour. O/S plug black and sooty. I’m feeling that its a coil failing under load so will swap out coil when spare arrives, hoping I can face removing tank for what seems the umpteenth time.
This is spooky - sounds like we are encountering exactly the same problem, trying the same things and getting the same results!
During the process of trying to resolve the o/s sooty plug issue I have discovered many issues (leak to n/s carb inlet, helicoil o/s spark plug hole, replaced failing elec. ignition with points, new plugs, ht leads and coils.) I still have a sooty o/s plug and am returning 34mpg.
I also dismantled the carbs, cleaned, replaced seals, checked jets/needles.
The general consensus from those with more knowledge/experience in these matters than me, is that the o/s exhaust is too restrictive.
It is apparent that the silencer has been damaged by the bike being dropped at some time prior to my ownership. The baffles are tightly packed and may now be proving to be too restrictive.
Am plucking up the the courage to invest in new silencers …… Will report back when I have done so.
Good luck with your bike and thanks for keeping us informed.
I’ve tried to upload images of the plugs. The ones on the blue paper are after the dropping down onto one cylinder.
The other image is of the darker O/S plug.
Is your plug this dark?
The choke plungers are what I replaced, showing the tired rubber seals. They weren’t in the carbs when the last run was done.
The bike is running a Rita ignition. I’m running with the perhaps naïve notion that this either works or doesn’t so the other option is a duff coil?
Just tried both plugs resting on heads, cranking over there is only sparks from the near side.
Measured both coils,copper leads, 5k plug caps with meter, results the same. Ergo faulty Rita.
Can send unit off to Rex’s for repair/ upgrade or , I have a spare points dizzy which I can replace bearings springs etc
Any thoughts?
