180 seemingly dies and comes back

mar

mar

Hero member
Location
California USA
My 1982 Mirage has started doing something strange. It will run just fine and then will run as if it is running out of fuel. When I switch the reserve, no change. The pecocks are new, the carbs are newly rebuilt, it has a modern electronic ignition box. This will continue to run like this for 20 or so miles and then return to normal. Valves are spot on.
When it occurs I have tried to open gas cap to see if mabye the issue is venting. No change. Plugs are fairly new, about 6000KM.

Any suggestions ??
Thanks so much, Myke
 
Well before splashing out on bits, do a bit of diagnosis!

When the symptoms exhibit themselves, at least stop the bike and whip the plugs out (at least the outer plugs).....take a picture and report back :-)

And check if you've got a "cool" downpipe (be careful....they're HOT....I'm sure you know this).....and report back :-)

One last thing, is it a single pull throttle cable on an '82?? Or does it have a splitter.
 
I had a RGA Jota Sprint fitted with a Witt ignition that the regulator/rectifier (the ones that never go wrong) developed a fault that gave similar symptoms to this. Thirtyfive quid to Electrix cured it nicely.
 
I haven't gotten back to looking at the Laverda as of yet. I will look at it this comming week-end.
This past week-end I had issues with my car and that took up most of my time. :'(
 
It can only be lack of fuel, spark or compression.

Any chance there could have been crud in the tank and now in the carbs?

From:http://www.laverdamania.net/carbgb.htm
- Dirty carbs, blocked galleries
In this case, check the mixture screw/pilot jet/progression galleries. in the abscense of a compressor a full tin of carb cleaner used with the extension tube will usually do the job. Check for flow through the
two little holes either side of the edge of the throttle slide nearest the engine. With the extension tube up the pilot jet hole you should get a jet of cleaner through both these holes (credit Steve Winterton)

On the lack of spark front, something like this between lead and block will show up a missing spark
http://www.etoolcart.com/gunson-flash-test-ignition-tester-g4079.aspx

Compression test wise, test compression first. if any look low drop a top of engine oil down the bore and re-test (if compression comes up the bores/rings are worn, if not the problem is with the valves or head gasket)
 
IMHO,none of the above

more likely to be,one or more sticking valves, manifesting itself when you put a little more heat into the motor,(ie giving it a thrash) which then returns to normal as the motor cools again, could also be a cylinder bore/piston too tight, for the same reason.

Have you had the motor apart rrecently and done some repairs?
CLEM
 
Agree with Clem as serious possibilities to consider!  Seen it often many different types of engine, exactly as described!

Julian
 
Did it only start after the recent carb rebuild? Is it only doing this at a constant/steady throttle position and rpm? Have you tried giving it more or less throttle(you can just change gears to do this) to see if it returns to normal power right away?
 
Clem, the motor is bone stock; no rebuild.
Henry, the carbs were rebuilt when I assembled the bike last year. The have been working great all year .
The fuel lines have industrial tractor filters on them and they are still nice and clean.

It doesn't usually occur when I am on the throttle and getting the motor hot. It has occured when riding at low RPM, say around 3K to 5.5 K.

I did just have the valves adjusted and they were quite tight. Now they are ( I am told) spot on.

Myke
 
the last time I had my Guz serviced "professionally" about 8 years ago (because of lack of space and time) there was definitively something wrong when I got it back and didn't ride it until 5 years later I had again space to tinker.... valves hopelessly out of spec and if this was the only thing... almost no oil in the gear box and nearly not enough in the engine and carbs not balanced properly. So far for a professional service...

I would take your bike back and complain it drives like rubbish in lower revs since the valves were done
 
When you say that the valves were tight do you know how many miles had been covered since the previous valve adjustment?
 
looks like we are getting closer, the valves have been adjusted, so first point is to check those clearances again, and tell us what they are.

The next thing is perhaps a tappet has had its bore damaged in the clearance change process, even a slight nick can cause a tappet to stick and this could then hold a valve open,even slightly open, or the wrong tappet had been fitted in the wrong bore, which gives a clearance error as well,it is important that each tappet is dropped back into the bore that it always ran in.I always hang the tappets upside down on the nearest stud, so no mixing up I would say your problem is valve related,

remote, but again a possibility is a broken valve spring, this could make the motor run OK, but not "keep up" when you start to "give it a bit more welly"

CLEM

ps f.w.i.c.
tappet = valve bucket
 
bclark said:
When you say that the valves were tight do you know how many miles had been covered since the previous valve adjustment?
Click to expand...

When I bought the bike last year it had 11000Km. They bike had been owned by a friend of mine and he had the valves adjusted at around 8,000Km. I just had them checked at 18,000Km. They were quite bad.
However the bike sat in pieces for what may be over 20 years. The motor , however, was never taken apart.
 
check the valve clreances right now then, dont ride any more until you have done it, but ,it has to be said that a motor sat untouched for a very long time could easilly have some corrosion on a valve stem (possible exposed through an open valve), and cause this grief, I suggest again, check the clearances and turn the motor very slowly by hand (no plugs no valve cover), and see if you can hear a valve "clack" as it catches back up with its cam lobe after sticking, but *(agaian0 that might only happen when it gets hot.
CLEM
 
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