Hi tiger_cub, That is often the sign of a clogged idle jet. Low voltage will mess with Boyer
timing curve. Valve adjustment & base timing need to be verified good. You may have multiple problems.
Morgo 750 kit will run perfectly with single carb & Boyer
on 1970 Tiger. I know that for a fact from personal riding experience on a '70 Tiger with your set up. But... has new Premier as old was worn out. It starts perfectly also. Actually this is a very desirable combination.
Look into carb, air filter off. Hold full throttle. Verify choke is actually all the way up. Move lever & watch choke go up/down to be sure it's not binding.
How is valve adjustment? It must be verified good. That is a prerequisite.
Battery voltage MUST be 12.6v or more key off. Good voltage is imperative with Boyer
Timing must be checked with strobe once you get it running. However, look at the Boyer
(on line if you don't have one). Set the static timing dot on rotor per the manual
. This will allow bike to start & run even though timing is not perfect. If... you can't get the dot to show, you must remove pick up plate & rotate rotor on the exhaust cam taper. The Boyer
rotor is not keyed to the cam like the original points AAU was. You have to mark where it is with felt pin. Pop it loose, then rotate in the direction where you run out of slot. Trial & error basically. A TDC tool is very helpful in lining up rotor & pick up plate. Or use timing mark on alternator rotor. Takes some practice & fiddling sometimes. Then after bike is running good enough set timing with strobe light. You may need to move rotor again if you didn't go enough the first time. Run motor at 4000rpm to read timing.
I like to set timing slightly retarded with strobe light. At 4000rpm the line on rotor ends up 1/64" towards rear wheel past pointer. That's about 36b. If timing is too retarded it makes bike hard to start & runs poorly.
After the Boyer
static timing is set so dot shows as it should you're ready to start & see how it runs. Should start well & run decently if carb is ok. Even though you still need to do strobe timing after you get it running good enough to strobe timing.
Getting to carb, make sure no air leaks at intake manifold gaskets & carb gasket/o-ring depending on what you have. '70 Tiger would have had the fat o-ring set to air gap of
.040-.060". I like about .045". If you use phenolic spacer, make sure gasket is there on manifold side & skinny o-ring in carb groove. Whatever, no air leaks.
Set mixture screw 1.5 turns out. Slide 3 should work good. Needle position won't matter until you are under load & riding with throttle open enough to uncover the straight part. Main jet won't matter until 3/4 throttle or so. You may find the bike works better with clip on bottom groove of needle, but that won't effect your problem now. Verify the needle clip is indeed properly trapped under the spring & not winding up the spring.
Is this a new AMAL
Premier or old original AMAL
? The float level is different. Verify the float is not catching on anything. If you still have old plastic float & needle I most strongly recommend replacing both with Stayup float & aluminum needle with Viton tip. From AMAL
. However be careful spending $ on old carbs as if slide & bore are worn it will never work right & die at idle. Still even with great wear it will usually start & run at least decently.
If all the above is good the idle jet & passages must be verified to flow well. To do this remove carb & remove bowl. Remove mixture screw. Remove jet holder, main jet & needle jet. Place plug in the idle air hole at carb mouth were air filter screws on. Put 2 fingers in carb & block the tiny fuel holes on floor of carb. Put stem of carb cleaner can into the passage under carb where idle fuel comes up through bowl gasket. Spray cleaner into hole. Cleaner should freely flow out of mixture screw hole, flowing through idle jet. Now blow cleaner through idle jet. Fuel should freely flow back into bowl passage. If nothing the jet is blocked. In any case take a piece of wire, strip it back 4" & cut 1 strand out. Look real close & stick that strand into idle jet. Make sure it really goes in through the jet. The jet hole is .017". If you can measure wire it must be thinner so can pass through. One wire is in wiggle it around to dislodge anything. Trial & error as you can't see or access the inside passage. Now blow carb cleaner into mixture screw hole, still keeping all 3 of the above passages still blocked. Use compressed air if you have it of course. Now blow carb cleaner through the idle air hole in mouth, the 2 small holes, the idle fuel hole on bottom & the mixture screw hole. Blow back/forth until you see all passages flow cleaner perfectly.
If crust is inside the hidden passage. Dry carb well as you can. Soak for 30 min. in white vinegar, turning carb & making sure vinegar is actually getting into the hidden idle passage. Flush with hot water. Compressed air if possible. Flush with carb cleaner spray again. If you get floating debris inside this passage you can finally work it out with vinegar & compressed air. I've done several.
If you have Premier carb the idle jet should be .019. The Premier has many changes & needs larger idle jet. Float level is above & parallel with float bowl gasket. Very different from 1970 Concentric
which is .070" below gasket surface.
Generally if mixture is correct motor will start perfectly, but idle will be low & not reliable until motor warms up.
With a good tickle until gas flows down side of carb, no throttle, kick bike & as it begins to fire, give throttle & work throttle to keep it running until warm. About 10 min. The will idle fairly well & take throttle well. Choke is often not needed until you get down to the 30s. But when cold some choke will help motor take throttle better until warm.
Hot start is another matter. On warm/hot days bike may be hard to start after parking 5-45 min or more. The cure is tickle carb, hold full throttle & kick hard. Be ready to back off throttle as motor will rev fast. Will not idle until carb & motor temps stabilize. 2-3 min. Blip throttle. This is very common with modern fuel on old bikes.
If everything else is perfect. Mixture seems good. Bike wants to stall at stop lights or sometimes stop signs. Or wants to stall just taking off unless you give it more throttle than you'd like. Also sometimes in stop/go traffic rolling along at 15 mph or so traffic picks up slightly, you gently roll on throttle, motor hesitates or actually dies. Motor is fully heat soaked after 30-40 miles. You are stopped idling. You turn throttle very slowly lifting slide on a tiniest amount the motor dies. May or may not be hard to start under any of these dying. These are the symptoms of a worn slide & bore. Replacing slide may give some improvement or not depending on how worn bore is.
New Premiers work really well. Email AMAL
directly. They will custom assemble Tiger carb with the slide, jets, top, banjo etc. you want. No extra charges. Many sellers have generic Premier that may or may not have what you need. You must verify from seller what slide, jets, including idle jet. Idle jets are visually identified by the number of grooves machined in jet snout. There is a chart to know what is what by the grooves. I would start with needle clip on bottom groove with new carb also.
Good luck on this. Can be a fight.