Dellortto carbs, idle increases once engine gets hot?

Paul LeClair

Paul LeClair

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Location
Calgary, Alberta, Canada
Hi all

very final stage of fettling the 82 1200 TS Mirage Series 2, hopefully.

the engine is breaking in nicely, but.......

when the engine first comes up to temperature and the choke is turned off the engine idles nicely at around 1,000 rpm. However, during a longer ride, or in heavy traffic, as the engine heat rises the engine idle increases from around 1,000 rpm to 2,000 + rpm and stays there.

I used brand new choke plungers when I rebuilt the carbs, and in my search for a perfect idle I went from 55 pilots to 60 pilots to now, 65 pilots.

I am using the metal intake manifolds (with new O rings and a dab of high temp sealant) with the rubber carb connectors secured with two clamps, and the rubber carb connectors are new.

Ignitech ignition is dialed in perfectly, valve clearances are spot on, carbs are vacuum synchronized, the carbs are hooked up to the stock (gutted) air box, and the exhaust system back on the bike is the stock restrictive LaFranconi's.

I am at a loss as to what to check next. Suggestions?

Paul LeClair
 
Can you turn the idle down with the idle screw? It's a remote possibility but is the throttle cable adjusted to zero play when cold? Engine/carb expansion from the heat could maybe cause the cable to open the slides a tiny bit. Or an air leak from a tiny crack in a carb body or the head? You could try spraying some carb cleaner on the carb bodies/intakes/cyl. head when it is hot and see if there is any change in the idle. Pin point spray [small qty's] to avoid it getting sucked in through the airbox and confusing things.
Another possibility would be a slide hanging up from a warped carb body but that may be more remote than the stuff above. Good luck!
 
Paul: Your a Sick Breganzie Enthusiast - Yah! It sounds like worn out worn Cylinder Bore and Ring Gaps and Casing seals. The Engine is too weak.

Doesn't mean you can't keep the the original pistons with a straight hone and gap with over sized rings and touch up the Valves and seats while your at it.

On the other hand it could be as simple as jetting the Dellorto's jets richer at Idle.

Are you leaning out after 5000pm?

Breganzies hate Exhaust Pipe changes and you got to re-jet the Delllotos until the fuel sand off has a rich stink at idle.
 
Going through this at the moment. There is quite a bit of change with slight changes to the advance map around idle.That worked for me for a while but after a week or so I am having an idle around 1800 when the bike get hot in traffic.I used to have an extended idle ajuster on the Kehan CV carbs and I loved the way it worked.So this morning I took the idle knob off The Mikuni Flat Slides I have and went looking at the wreckers for a replacement extended cable type adjuster. Dont know if this will help your setup Paul.I found a Fireblade one that is close,wrong thread as the Flat slide one is Metric fine and the Fireblade one is metric course.. Before doing this a rang the Mikuni Distributer to see if they had anything to suit. They had nothing except a lecture about if the carb is set right the idle does not change.That's NEVER been my experience. Set it cold and it rises when the bike is hot. Set it hot and the bike stalls without throttle when cold.
Being able to change it easily is the way I am going.BTW my bike does need a little more jetting adjustments as well.Mix screw tweeks I expect.
 
Vince said:
Set it cold and it rises when the bike is hot. Set it hot and the bike stalls without throttle when cold.
BTW my bike does need a little more jetting adjustments as well.Mix screw tweeks I expect.
Click to expand...

In actual fact all you should be adjusting your idle when the bike is at operating temperature as if you set when cold it will be too rich when hot then when it warms up the idle will be all over the shop.
Vince are you sure that your return cable is adjusted correctly and yep would imagine that a bit more tweaking on the mixtures would help, as I understand those Mikuni's they are very very sensative so little by little but again when warm.

Guess that is another plus with the throttle locks that I use hey as when cold just flip it on with the throttle cracked a tad.. works like a charm which reminds me guess the Cico is due for one now too though with the smaller choke jets it can hold the idle on a slight amount of choke and not foul the plugs.


 
Laverda SF said:
Paul: Your a Sick Breganzie Enthusiast - Yah! It sounds like worn out worn Cylinder Bore and Ring Gaps and Casing seals. The Engine is too weak.

Doesn't mean you can't keep the the original pistons with a straight hone and gap with over sized rings and touch up the Valves and seats while your at it.

On the other hand it could be as simple as jetting the Dellorto's jets richer at Idle.

Are you leaning out after 5000pm?

Breganzies hate Exhaust Pipe changes and you got to re-jet the Delllotos until the fuel sand off has a rich stink at idle.
Click to expand...
Its a fcking new motor Ron, keep up old fella
 
OK COSI! I don't keep up with the forum but my diagnostic may be relevant to the OP.

All I'm saying is that a tuned Breganzie literately spits Stand Off Fuel through the Dellorto carbs for an 800 rpm Idle.
 
Vince said:
Going through this at the moment. There is quite a bit of change with slight changes to the advance map around idle.That worked for me for a while but after a week or so I am having an idle around 1800 when the bike get hot in traffic.I used to have an extended idle ajuster on the Kehan CV carbs and I loved the way it worked.So this morning I took the idle knob off The Mikuni Flat Slides I have and went looking at the wreckers for a replacement extended cable type adjuster. Dont know if this will help your setup Paul.I found a Fireblade one that is close,wrong thread as the Flat slide one is Metric fine and the Fireblade one is metric course.. Before doing this a rang the Mikuni Distributer to see if they had anything to suit. They had nothing except a lecture about if the carb is set right the idle does not change.That's NEVER been my experience. Set it cold and it rises when the bike is hot. Set it hot and the bike stalls without throttle when cold.
Being able to change it easily is the way I am going.BTW my bike does need a little more jetting adjustments as well.Mix screw tweeks I expect.
Click to expand...

Hi Vince and all

I have a basic ignition map that Lex provided me for the Ignitech, and I have not fiddled with it at all.

The carb bodies and slides only have roughly 6,000 miles on them from new, I replaced all the brass, needles, etc, and have not had this particular rising idle issue with either of my other Laverda triples. I set up and tuned this bike using the same processes I have used on the two other triples. Something is going on that I have not figured out yet.

the advice to check the carb bodies for leaks is a great suggestion, I do have another older set of Dellortto's where the very fine crack in one of the carb bodies is not even visible until you "flex" the carb body by pushing on it while it is on its manifold, I'll try spraying for air leaks while the bike is running.

Adjusting the idle mixture knob under the tank on the Dellortto's when the engine is running is a burn hazard, the knob is tough to get at and tough to turn without cooking a hand, not something I want to be doing with any regularity. I need to solve this for a stable idle.

Weather here turned viciously, went from 21 C earlier to day to a terrible brutal wind storm with a forecast of snow and minus 2 C overnight and tomorrow, so no test riding tomorrow, although it is supposed to warm up again for most of next week. I am focused on getting this issue solved before the bikes have to be put away for the winter.......

Paul LeClair

 
Weather has drastically changed with in the last day or so here on the North Shore as well - Good Luck with your trouble shooting.

We had a HOT summer here but hopefully we get an Indian Summer into November ;o)
 
Burn hazard? Come on Paul, man up.
Not that hard to reach when off the bike and certainly possible without a trip to the burns unit.

Make sure, as was said, there is at least some slack in the throttle cable.
My money is on the carbs having been initially set when the engine was not up to temperature so that when it reaches that temperature it idles higher.
A cold engine should need choke at the start, but if it doesn't really need choke to idle when cold it means the carb settings are rich and compensating for lack of choke.
Set the tickover when it is warm and deal with lack of idle when it is cold.
 
Paul LeClair said:
Hi Vince and all

I have a basic ignition map that Lex provided me for the Ignitech, and I have not fiddled with it at all.

The carb bodies and slides only have roughly 6,000 miles on them from new, I replaced all the brass, needles, etc, and have not had this particular rising idle issue with either of my other Laverda triples. I set up and tuned this bike using the same processes I have used on the two other triples. Something is going on that I have not figured out yet.

the advice to check the carb bodies for leaks is a great suggestion, I do have another older set of Dellortto's where the very fine crack in one of the carb bodies is not even visible until you "flex" the carb body by pushing on it while it is on its manifold, I'll try spraying for air leaks while the bike is running.

Adjusting the idle mixture knob under the tank on the Dellortto's when the engine is running is a burn hazard, the knob is tough to get at and tough to turn without cooking a hand, not something I want to be doing with any regularity. I need to solve this for a stable idle.

Weather here turned viciously, went from 21 C earlier to day to a terrible brutal wind storm with a forecast of snow and minus 2 C overnight and tomorrow, so no test riding tomorrow, although it is supposed to warm up again for most of next week. I am focused on getting this issue solved before the bikes have to be put away for the winter.......

Paul LeClair
Click to expand...

Then you haven't overhauled the carbs completely, Paul

I often come across stiff screw action through accumulated crud etc.  If necessary, run a tap through the thread on the bracket, a wire brush cleans up the screw thread nicely..Once cleaned and freshly lubed, the screw moves quite easily.  A drop of oil on the ends of the spring works wonders as well, especially if you have a plastic knob (oh dear, that will bring up comments, won't it!).

I find access to the screw quite OK, having it turn freely makes adjustment easy.

piet
 
It can be a bit hard to reach if you are sitting on the bike...  :D standing on the right side of the bike, reaching in with your left hand should be no issue at all.

when you overhauled the carbs, did you also exchange the "cotton" type seals of the actuation rods in the "dome"? Did you grease them slightly? air may pass there... also check the little hex-screws that fixes the lever that pulls the sliders up and down under the top-dome cover is fixed and secured with a dip of Loctide. Next, make sure the choke sliders all move at the same time and do fully close the hole that you can see from the back side of the carbs (remove the rubbers to the airbox, stand on the right side of the bike and look into the open side of the carbs, you will see the sliders moving on the left side of the carbs if you open/close choke reaching the choke lever with your right hand).

Also make sure the float hight is correct and the float needles do close fully. Wrong float hight can cause either leaning of the mixture or overflowing of the carbs. Having to go up in idle jet size could point to to low float level...

BTW: are you using fuel filters? if so, they could have the wrong throughput... Have you checked the filters in the tank? Possibly water in the fuel system?
 
Paul LeClair said:
... when the engine first comes up to temperature and the choke is turned off the engine idles nicely at around 1,000 rpm. However, during a longer ride, or in heavy traffic, as the engine heat rises the engine idle increases from around 1,000 rpm to 2,000 + rpm and stays there. 
Click to expand...
I suggest the Dellorto carburettor bodies are still relatively cool when the engine first comes up to temperature. no ??

All of the carburettors need to be 'up to temperature' or i find it's just a waste of time.  Just saying.
 
Brett said:
... you should be adjusting your idle when the bike is at operating temperature as if you set when cold it will be too rich when hot then when it warms up the idle will be all over the shop.
Click to expand...
What he said!! You will NEVER get a smooth idle at op temp if you set it up to idle from a dead cold start! if it idles beautifully when dead cold it's running way too rich once hot. Modern (mostly fuel injected) engines have a fast idle sys connected directly to a temp sensor that regulates everything automatically - best way to warm it up quickly is to start it and ride off - it will reach op temp a lot quicker than idling it in the driveway.
 
got our first snow of early fall here overnight, can't ride today, so carb rack is coming off and apart to see whatever there may be to see.

all good comments in this thread, thanks, I will take everything into consideration.

I did clean everything thoroughly when doing the carb rebuild, everything had a good soak in Gunk HydroSeal 2, then a few passes through the ultra sonic, and I did run a thread die on the idle adjuster threads as I usually do. The issue for me adjusting the idle adjuster on a hot engine without burning myself is unique to me. When I was younger I was in a fire that left me with a lot of burn scars and grafting scars, including extensive skin grafting on the back of my right hand and up my right arm, resulting in a lack of feeling in my right hand and arm. I don't feel it when I cut myself or burn myself, so I avoid situations where I might damage myself without knowing it, including not sticking my hand into the hot area behind the engine....... I have tried gloves, but they seem too bulky for the task. I have developed all sorts of coping strategies over the years, the best of which is just to avoid potential damage, I got sick and tired of noticing blood dripping on the floor as my first indication I had damaged myself again..

I am ready to be done with fettling this rebuild but wound up with another flat battery on a brand new Odyssey PC 680 this morning, so obviously have some sort of charging or battery drain issue to find as well......  my bet is on yet another bad relay sucking power while the ignition is off, I just had that happen on the 79 1200 with the same brand of relay in the horn circuit, maybe got a bad batch of relays........

Paul LeClair
 
got our first snow of early fall here overnight, can't ride today, so carb rack is coming off and apart to see whatever there may be to see.
Click to expand...

So SNOW is coming my way - Hope you get an Indian Summer to play with it more.

I gotta FIX the Front Drive Shaft on my Jeep before Snow stays so I can use 4WD in the it.

Wish I had a Leyland Land Rover but can't afford it. On the other hand Jeeps a cheep to fix if you can understand the shit!
 
Paul, before you rip the carbs off, you don't need to ride it to get it up to temp, get it really warm, turn it off, let it heat soak for 5 minutes and run it again; keep doing that until you get the fast idle you described.
Then adjust it down to 1,000 rpm or so, run it a little more, and see if it settles at the 1,000 rpm's
Then let it cool a couple of hours; I bet you'll need a lot more choke to get it/keep going!

Fingers crossed
 
Paul
The best way is to warm up by taking it for a run, understand your hand/arm issue but you can do it with your left hand with a bit of practice plus you need to tweak the mixtures.

Trouble with doing it wiht the bike static and only idling etc especially if it is for a while of playing around is that you can get unburnt gasses building up and causing a negative effect fouling plugs etc... .........

Usually best to get close then take it for 10 or 15 min run then fine tune.
As before when cold live with it ................or use a throttle lock then you best of both worlds.
But then again what would I know

What you should have done was get Marty to do it when he was there..... that way no drama on your arm.

Cheers
 
The SF1 I've been riding pops and farts for a bit after riding off (only from a closed throttle). It's a bit annoying but it quickly reaches op temp and the idle settles - carburation once hot is spot-on. Having a friction choke lever (ie infinite adjustment) makes it a bit easier but I avoid riding at all on choke.
 
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