RGS Won't Rev above 4,000

2

2Types

Junior member
Location
Wales
Have a new to me RGS which has not seen much use over recent years. It seems to run ok until it gets to about 4,000 and then starts missing and not going any higher back off and all seems ok below that. What are the most common things I should start with first.
 
Check/Clean the carby float bowls ( water in the mains, idle pilot is lower in the float bowl so water usually is across the rev range ), if able remove the main jets and inspect the size and obstruction free orifice... staged process, what does it rev like when on the center stand BTW.
 
if not carbs related (which is also what I would look first at), it can be:

-old patrol with water in the tank => exchange completely!
-tank breather blocked (and before someone says that would stop the bike completely: it can breath a bit through the tank-cap, too, i think)
-if still having original ignition or one that uses the original pickups, it can be the pickup-cables
-ignition coils need exchange

I had more weird ones like a fuse "dancing" in to wide contacts, but I would first look at the above and start with the easiest and most obvious ones
 
Hopefully your not a dumb fuck like me. Many years ago I did a rebuild on RGS and did not ride it for two years or so as the work was underway. But at least I had my modern bikes I did ride during this period.

Upon my maiden voyage on the RGS after the rebuild thru town all went well but when I hit the highway I too could not get it to higher revs and speeds. After a a km or so of thinking what did I do wrong on the rebuild...wiring....carbs...fuel taps etc ....I remembered you needed to grab a second handful of throttle to make it go. Did I ever feel like a dumb fuck considering all the years I had Laverdas and other older bikes without the quarter turn throttles my modern bikes had. At least it was an easy fix!
 
Took the float bowls off and main jets out - nothing obvious but gave everything a squirt of carb cleaner and reassembled. Now revving freely.

It does seem to be running rich and when I was poking around it struck me the air intake is quite compromised. On the inside the crankcase breather goes up in front of the intake. On the outside there are a couple of cables and the battery sits very close. It appears a correct battery but sits higher than the inlet so would foul the trumpet if that was still there.

My other RGS has a couple of large holes in the bottom of the airbox. What is the best way to improve the breathing but still keeping an air filter and ideally the airbox.
 
Can't be the correct battery if the trumpet would foul it. Or it's sitting on too thick a mat.
Typical mod is to remove crankcase breather gubbins and route suitable hose to back of the bike. Some folk use the earlier breather pipe that directs to rear chain.
Another mod is to drill a couple of 40mm holes in bottom of airbox a la Corsa.
Obviously make sure air filter is clean 😉
I believe the air trumpet is worth fitting but many don't.
Finally, the needles and atomisers take a pounding from pulsing airflow and their wear results in rich running. Check choke cables have free play and the choke rubbers seal. Also float level adjustment is critical to good running.
 
andre said:
What ignition does it have? I recall I had a problem like yours with a early dmc
Click to expand...
It has the standard BTZ and I did not touch the ignition side as wanted to try and do one thing at a time. There must have been a small blockage or a stuck float which I could not see but cured with taking the float bowls off and squirting Carn cleaner in all the jets
 
2Types said:
Have a new to me RGS which has not seen much use over recent years. It seems to run ok until it gets to about 4,000 and then starts missing and not going any higher back off and all seems ok below that. What are the most common things I should start with first.
Click to expand...
Under the gas tank is a bracket that holds 3 coils which send electrical charges to the spark plugs. That bracket is made of a soft metal that will fatigue over time and vibrations from riding about. Check that bracket for miniscule like cracks. This can cause the engine to break up over the mid-range of the RPM. Due to the cracks it can lose its ground. It is grounded to the frame.
 
The cracked RGS coil frame having an effect on the ignition circuit paths is not as it would seem, the only coil with a pole centre secondary winding frame return was the dreaded Motoplat red coils, even then there were two variants of the same outwardly looking Motoplats.

Would be well surprised to believe any are still in use, only two sets i saw and took two days to diagnose were on a first gen ( black wheel ) Corsa. Replaced a number of coil frames over the years, with genuine home baked 2,5m/m aluminium bespoke wonderful and very attractive frames.... i would say that would'nt i.... tah Mandy Rice Davies... lovely turn of phrase from the poms... j
 
My one and only electrical save was that. I was limping home from a Snowy Ride with the club via The Princess Hwy with a pretty bad oil leak and stopped for fuel and lunch in the middle of nowhere. And the bike wouldn't start, I pulled all the luggage and the petrol bloke gave me a push with again zero results so I had a fiddled around to find no spark at all. I did the wiggling wires and nothing. As a last resort I tightened the coil mount and baggar me the spark came back. Loaded back up and made it the 400ks back home. Around then I had a full rewire and that helped a lot with my confidence to get home.
 
stevepm2011 said:
Brett,

All o-rings are new, as are the inlet manifold rubbers.
All jets are new.
Floats are good and level is correct.
Exhaust is new, standard, no leaks.
Air filter is standard, and I still have the snorkel on it.
Checking the DMC earth is a good idea.
I synch at idle, but check it stays good as you open the throttle.
If all else fails, I will rebuild my spare set of carbs, and swop them out

Anyhow, I need to finish off fettling the 1000 SFC, because I want to ride it to the Heftrich rally, then I will have another go at the RGS.

Thanks for the suggestions

Steve
Click to expand...
Picking up on an old thread which describes my issue exactly. Have also read a number of other threads on jetting etc but I have the very same issue of not liking very small throttle openings and there seemed to be no conclusion here

Set up is
Jota Pipes
standard air filter, no trumpet, 2 x 35mm holes in bottom of airbox
108 mains
65 pilot
Floats all at 18mm

It did have I think 118 mains but hard to make out on 1 and no markings on others so went to new 108s.

Main symptom is when using very little throttle in say 2nd gear at 3000rpm starts to feel like fuel starved which gets worse as builds to 4000 rpm which can be annoying when coming out of a slow roundabout in traffic. I have done all the checking for air leaks, recleaned the carbs, checked all little passages clear etc. Needles look as new and atomiser look relatively new but I cannot be sure. Float needles look very recent.

Mixture screw is a fraction under 1.5 turns out. a further 1/4 turn made no real difference and a further 1/4 ran far too rich. It is currently about 1/8 turn in from where a non-Laverda mechanic set it. I found this setting best for idle after a good run so bike was fully warm.

Plugs are ok but due to time my runs have been a bit short and at constant speed I think it is a bit lean, but at low revs/idle could be a bot rich.

I have a new set of 115 mains I intend to try next. From what I have read I think these should be the max I need. I am not hopeful as probably took out 118s when the problem still existed, although no genuine dellorto so worth a try.

After that was going to re-check the balance and maybe then try moving the needle up a notch. I could keep replacing needles, atomisers etc in hope but any more targetted thoughts welcome.
 
Have you carried out basic service / checks? Valve clearances, ignition trigger gaps, carb balance, new plugs?
What about the checks suggested above - in particular choke plunger condition & cable free play?
Can't see your answer to iis_iis question re revving OK in neutral. Without answers to points raised in response to your query we're shooting in the dark on this.
Have you carefully inspected trigger / pickup wiring including the 6 way connector block at the back of the crankcase? Wiring insulation gets brittle and flakes off with age. Connector can corrode.
Your problem is nothing to do with main jet size. As you have found, 65 pilot is a bit too large but again can be sorted by the idle mixture screw
 
I bought an RGS a few years ago that had been unused for awhile. It had a similar issue. The problem was the choke, but not necessarily the answer to your problem.
 
Rob said:
Have you carried out basic service / checks? Valve clearances, ignition trigger gaps, carb balance, new plugs?
What about the checks suggested above - in particular choke plunger condition & cable free play?
Can't see your answer to iis_iis question re revving OK in neutral. Without answers to points raised in response to your query we're shooting in the dark on this.
Have you carefully inspected trigger / pickup wiring including the 6 way connector block at the back of the crankcase? Wiring insulation gets brittle and flakes off with age. Connector can corrode.
Your problem is nothing to do with main jet size. As you have found, 65 pilot is a bit too large but again can be sorted by the idle mixture screw
Click to expand...
Thought I had (confusing when working on two RGS at the same time but rechecked the trigger gaps and they we 0.15mm and other two <0.05mm with some evidence of touching. Now reset and running better.
 
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