Moto Grand Prix
Main Motorcycle: 1973 Triumph TR7RV
Join Date: Oct 2013
Location: Pleasant Hill, CA USA
Other Motorcycle: 1964 Triumph Mountain Cub
Hi Stopngo, Start by verifying the choke is not accidently stuck on. Look into air horn of carb & give full throttle. The choke slides should be full up with choke off.
Verify the throttle slides lift evenly or at least very close, & close freely.
The '68 Bonnie has dual points. The timing is set individually for each set of points. What backing plate does you points have? You should have the 6CA late type points plate. On this late version the backing plate has 2 sub plates screwed to it. The points are then screwed to the sub plates. This allows you to set point gap to .015". Then each points mounting plate can be moved independently to set timing. If you find you lack range of movement on a sub plate, you rotate the main (round) backing plate as needed. Then start all over with gap & timing each set of points.
Just in case you have early type points plate. It's just round plate with 2 sets of points screwed to it. You set gap. Set timing on one set of points by rotating backing plate. Then adjust point gap of other set of points to set timing for those points. Still keeping gap relatively close to spec. A little tricky, but doable. Triumph started with the easier system for model year '68 so you should have the late points/plate.
In the photo there is a hash mark on end of points cam at about 8 o'clock. Line up points rubbing block with that while gapping points to .015"
If timing is way off it will run quite bad or not at all. In this case starting with static timing can be very helpful. Then proceed with strobe timing. Static timing is covered in shop manual. It is important to power a strobe timing light from a separate battery, not bike battery.
Properly set & serviced points are extremely reliable & allow starting with a dead battery.
I know you said has spark both sides, but is it a strong spark & does it still spark at higher rpm than kick start cranking speed?
One thing you might have happening is the points are not closing strongly. Held open with finger nail or screw driver when released, the points must snap closed with a decided click & force. Verify this. If the points spring is skewed it can put pivot in a bind. This is very common.
Normally the front points is for left cylinder.
Also look very closely at the wires attached to points spring stud. The plastic insulator spacers must be good condition & properly placed. Sometimes on bottom of wire, the insulation wears thin & can short to the timing cover. Very common. You can put a layer of tape on it until it is replaced. Also look very closely, & visually inspect every inch of wires points, to coils. Actually look over every wire on bike for faults you can see like worn insulation or pinched wires.
Also the points contact faces must be perfectly clean & dry. Parts wash on a strip of copy paper works well. Even gas will work in a pinch. Rotate motor so points are closed. Open with finger nail & insert a strip of paper soaked in cleaner. Close points until they put tension on paper. Wiggle paper around. Then dry contact faces with strip of paper. Do this until no oil or black shows on paper. I cut paper in 1/4" wide strips 3" long. Alcohol works good too. But if really dirty the other seems better for me.
Points should allow for starting with dead or low battery, but what is battery voltage key off? A good battery makes for easier starting & better spark. You want to have about 12.6v or more. Charge battery if needed. Disconnect battery during charging so you don't over heat Zener diode.
What is your voltage to coils (both). You may be getting low volts to left coil for some reason. With poor voltage you can get spark with plug removed, but not installed during compression stroke.
If the carb tickles freely it's getting gas. But is the gas actually getting into the carb throat? That can be hard to tell. I'd remove idle mixture screw at least. Shoot some carb cleaner spray with the straw into the bore. That might blow the jet free. Hard to remove idle jet for cleaning with carb installed. Take bowl drain out when you do this. Compressed air into bore for mixture screw is very helpful, but again make sure bowl drain is removed. Often you can at least temporarily clear idle fuel passage doing this.
I would remove valve adjuster caps & verify you at least have clearance on all 4 valves. I know you said compression is good, but you need to leave no stone unturned. As was stated, you need to go back to basics.
If you have:
Air getting in through carbs
Fuel getting through carbs
Timing is correct or close
Motor will start & run. If it doesn't one or more of above is faulty.
You've got some work to do. Take your time. Verify everything is ok best you can.
Here is photo of the later points plate.
Last edited by TR7RVMan; 03-16-2019 at 04:31 AM.
Reason: changed sentences