T5 Running poorly

Hi All,
I have a 1985 T5,which i can’t seem to get running right.It has points ignition,which i think are adjusted correctly,VHBT30 carbs,which have been cleaned,adjusted to factory settings(info from guzziology),and balanced with my carbtune gauges,cables adjusted correctly too,and all seems ok there.The problem?Well the bike ticks over smoothly,is ok in the higher rev range(no revcounter on this,so can’t say where it starts to clear from,but at a guess 3500rpm plus).It runs really badly above tickover to this,backfiring,very poor throttle response etc.It is a non standard bike,and it’s been customised in the past,so there are a few non standard bits,integrated ignition/headlamp from a 60’s BMW,K&N filters(main jets are standard 130’s).Any suggestions greatly appreciated.


How long has it been doing this? Was this sudden or has it been ‘laid up’?

By the way if 850 & k&N’s then 130 main jet sounds about right for that, would normally be 120 with standard paper filter if memory serves.

Sounds like not enough fuel at quarter to half throttle, but can’t think how.

Air leaks around head inlet stub/carb joint?

‘Choke’ mechanisms OK?

A long shot ~ how old are the contact breakers? The contact surfaces last for yonks but the bit that rides on the cam wears out, and unevenly as well so the timing wanders all over the show. Guess how I know That can cause some weird behaviour like misfiring popping banging and lack of power.

did you set timing to right hand cylinder on distributor and then set left hand on left hand points plate ?T5 i like

Have you timed it correctly? The marker on the flywheel is for max advance at about 5000 revs.Carbs come to mind, it took me a few goes to get mine thoroughly cleaned out. The lower rev range is controlled by the needle, have a look see if this has worn or the jet could have gone oval, messing up the mixture. As mentioned above, chokes can cause problems, either not shutting properly or perished seals. Check there is free play in the cables at the top of the carbs when the choke is off. Then take the choke plungers out and check condition of the rubber seal at the bottom. These must be in good condition to stop the flow of fuel up the cold start jets.Have a check on plug colour as a guide.Check the needle is in the correct slot, or just try it in a different one.Mixture adjusters should be about 2 turns out, make sure they are the same both sides.Worth changing the condensors as the cost a few quid from a car spares store and can give funny effects when they are breaking down.Does it sound like one cylinder is a problem or both? Few ideas to think about.

Worth changing the condensors

Some good suggestion there folks,thanks.Might be my imagination,but i think i can hear a slight ‘wheezing’ sound somewhere around the RHS cylinder,but closer to the inner block,not the inlet manifold or the exhaust.I’m new to guzzis,so am i just hearing the crankcase breather exhausting?Sounds like i have to did a little deeper to find the root of this…!
BTW,if it turns out to be a carb/slide/needle/jet problem,are parts readily available for these carbs?
Thanks again folks.


Had this on a 1000 , in the end it was a sticking choke and a slightly out of whack throttle cable.

I would do the simple stuff first:-

Check for air leaks a good trick I learned was start it and get it warmed up then squirt W40 on the inlet manifold if the revs inc it has an air leak (very useful on rubber inlets as they do crack but y can’t see it)

Check the Throttles are in sync and the choke is not sticking, also there is a tiny “o” ring at the top of the choke fitting they can leak air.

If you are using K&N or similar filters check they are not aking at the carb inlet too.

OK that done check again the timing

Although this is to set up a Rita LOOK at the info re “Timing marks” as this is for a T3 (other 850’s are similar) the info re setting up the timing and the degrees per tooth on the flywheel is very very useful.

(NB there is also downlloads for timing discs that you can print/laminate and use)

Having checked al that then it wil be tappet gaps again info on that in Frequently asked questions.

IF all that fails then is a check of carbs themselves I guess.

I am sure others may add to the list but sometimes the simple stuff is best to start with there is lots of info re delorto carbs on the AIGOR site and delorto site , access from our “links” section

guzzibear2012-08-30 12:46:35

Yep could be choke leaking, had this on the Bee-Em once (sticking air valve, which is rotary in this case [Bing]) very similar roughness effect.

‘Wheezing’, yes mine does a sort of chuffing noise at idle, it’s the air hissing through nearly closed throttle slides, the K&N’s make it sound more(?) audible.


Appendix ~ just as an aside, I learnt to time ign at the static position, i.e. 0 - 2° BTDC (fully retarded obviously), apart from being easier it’s more conducive (spelling?) to low-speed tractability, or at least you can be more sure that it’s set up that way.

my t5 had got blocked fuel taps and stuck accelerator pumps

get the taps out and flush the tank through, then strip the acc pumps and clean them , check they move freely

Thanks again for the suggestions folks.Cleaned carbs again,tried new condensors,thought it was running a bit better,but i took it for a run,and it died completely about 2 miles from home.Got it back to the shed,no hope of starting.I checked the battery voltage at this stage,and it was only reading less than 1 volt!I’m starting to think it might be an ignition switch fault?
As i said earlier,the bike is a bit of a bitsa,with a 60’s BMW headlight with integral ignition switch.
Any more ideas folks?
As always,your advice/time is appreciated.


Is the battery charging OK? Are you sure the alternator is working properly?

Yes,no bother with charging,13+v at around 2500 rpm.And the battery seems to hold enough juice to start the bike if left unused for a few weeks.

I had a similar problem many years ago with a car. Turned out to be a sticking float valve. Now, to be honest, I don’t know if your carb even has one!Sticks closed, will tick over happily, sticks open runs if you are using the fuel fast enough…Took bludy ages to track it down, cost oodles of auto electrician time (all the symptoms pointed to electrics) and ended up with a new carb from a scrappy.

Yes I’ve had that too! Metal needle had worn a groove so ended up getting stuck in valve seat.

OK it’s all sounding like fuel starvation, could be blocked filter, which will let enough fuel through to make work, so to speak, but conk out when you actually want more fuel to make it go properly.

When you say ‘cleaned the carbs again’, what about the filter screens, tank tap filters, no dead beetles down the fuel hoses & owt like that?

Appendix ~ I suppose what’s in the tank is all petrol is it, no water or oil lying in the bottom?

Somebody else on here recently got a couple of pints of water with his last fuel fill-up!

Every single aspect of the fuel system has been cleaned at this point,my concern now is the lack of battery voltage.The bike cut out suddenly while idling at lights,did not feel like fuel starvation the way it just died.I’ve not been able to revive the battery yet,my optimate will not initiate charge with such low voltage,i’ll have to find another charger that might do it.Removing the fuel lines from the carbs,i get a steady flow of clean fuel-no sign of contamination.Also,it was running ok at tickover,and at higher RPM,just a BIG flat spot around 2500-3000 RPM(approx).Stumped for the moment!Fledermaus2012-09-22 01:14:34

You clearly have an electrical problem now,may just be the battery has died, they do sometimes.

Right so it’s been an electrical gremlin all this time.

Sounds like it’s not charging? Ignition will falter if not enough Volts

That BMW headlight is worth a bit in it’s own right if you ever wanted to revert to standard.