• The Roadster Factory Recovery Fund - Friends, as you may have heard, The Roadster Factory, a respected British Car Parts business in PA, suffered a total loss in a fire on Christmas Day. Read about it, discuss or ask questions >> HERE. The Triumph Register of America is sponsoring a fund raiser to help TRF get back on their feet. If you can help, vist >> their GoFundMe page.
  • Hey there Guest!
    If you enjoy BCF and find our forum a useful resource, if you appreciate not having ads pop up all over the place and you want to ensure we can stay online - Please consider supporting with an "optional" low-cost annual subscription.
    **Upgrade Now**
    (PS: Subscribers don't see this UGLY banner)
Tips
Tips

TR2/3/3A Missfire and Backfire

Graham H

Jedi Warrior
Country flag
Offline
It may be a good idea to go back to your overheating problem, have you checked the radiator for bubbles does it lose water when it overheats this could be a burnt head gasket which would explain the ticking noise. When you rebuilt the engine did you retorque the head?

Graham
 

sp53

Yoda
Country flag
Offline
If your timing marks where right on in your picture, I think you are a tooth off; I pulled my plugs and put the hand crank in place and set both marks right on, and my rotor is to the left of yours about a tooth. The flasher flashed and brightened that picture, the other pics I took where too dark. I can try more angles.

I know what you mean about getting the gear tooth to fall and swirl into place and have the oil pump in the correct location, but I would bet you are a tooth off.

steve
 

Attachments

  • DSCN0395.JPG
    DSCN0395.JPG
    3.1 MB · Views: 65
  • DSCN0399.JPG
    DSCN0399.JPG
    3.3 MB · Views: 64
OP
K

Ken H

Senior Member
Country flag
Offline
It may be a good idea to go back to your overheating problem, have you checked the radiator for bubbles does it lose water when it overheats this could be a burnt head gasket which would explain the ticking noise. When you rebuilt the engine did you retorque the head?

Graham
Since I reported the overheating, it's done it again. The coolant is clear and doesn't have bubbles, so I doubt it's a head gasket leak. Yes, I did retorque a second time. Today, I picked up some radiator flush which I'll run through it in a day or two. When it overheats, it loses about a cup of water or two out of the overflow tube.
 
OP
K

Ken H

Senior Member
Country flag
Offline
If your timing marks where right on in your picture, I think you are a tooth off; I pulled my plugs and put the hand crank in place and set both marks right on, and my rotor is to the left of yours about a tooth. The flasher flashed and brightened that picture, the other pics I took where too dark. I can try more angles.

I know what you mean about getting the gear tooth to fall and swirl into place and have the oil pump in the correct location, but I would bet you are a tooth off.

steve
The timing mark in my picture was dead on, so I could be off a tooth. Assuming I'm off a tooth, then rotating the distributor the same amount would compensate. There's no adverse affects other than the distributor rotated more than normal. Am I missing something?
 

sp53

Yoda
Country flag
Offline
I do not know if rotating would work. I guess you could move the wires on the cap or something, but I think you would have the same problem. I see it more as spark timing and would pull the shaft and move it.

The distributor pedestal needs to be removed to get the shaft out . Sometimes that comes off difficultly because the casting tapers on the bottom just a fuzz and sticks in the block. I use the hammer and block of wood with WD40 method if it does. I put them back on with one maybe two thin gaskets, but I have personally have not been overly concerned about the float of the shaft and the pedestal. I use a long screw driver to move the oil pump shaft and fiddle with distributor.

At some point, putting the distributor back in is art because I had visualize the blind rotating of shaft falling into the oil pump and messing the correct gear location by moving the rotor back to compensate for the twisting of the gears. Isn’t life great, no really we do get to work on these cars

steve
 
OP
K

Ken H

Senior Member
Country flag
Offline
Ken,
Regarding the idle setting. Although some owners attest to getting their car to idle in the 500-700 range. Mine do not and that does not bother me in the slightest. For initial tuning 800 to 1000 rpm is good.
Most of the sources I see recommend starting the timing at 4 degrees btdc. My friend, mechanic and long term TR4 owner sets the timing at about 30-32 degrees at 2500-3000 rpm with the vacuum advance disconnected. This has worked well for me over the years.
I use 87 octane fuel most of the time. I find little difference in the fuel octane.
I have 2 TR4s both cars are set up the same as far as I know. But one car definitely has more pep than the other. I have no idea why. It makes driving them interesting. I am just finishing a TR3A and will have it on the road next month. It is also set up the same as the TR4s. It will be interesting to see how it compares with the TR4s.
I have never experienced an erratic timing , so am no help there.
Glad you are working through what sounds like several variables.
Charley
Hi Charlie, Just and update. I ordered new carb piston springs from Moss and tested them against the original springs I now have to see if the original had weakened over time. The old springs turned out to be about 5% stronger than the new, so I'll keep the old and maybe have to put 40W oil in the dashpots.

I'm still playing with the Pertronix distributor. Their tech team says I must have at least 10V at the coil coming from the ignition switch. I tested mine and it's 9 volts. Looking at the circuit diagram, the wire goes through about 6 things before reaching the coil. I've been cleaning each connection (two are on the dash and very hard to reach) and with each wire connection cleaned, the voltage improves. Another day or two and I'll be ready to test their suggestions.
 

poolboy

Yoda
Country flag
Offline
Find the fuse that protects the green wire electrical circuits that are 'hot' ONLY when the ignition key is in the ON/RUN position... and test the voltage upstream of that fuse it should be the full 12 volts..
.That the location, upstream of the fuse is where the coil needs to be fed from.
 

charleyf

Luke Skywalker
Country flag
Offline
Hi Charlie, Just and update. I ordered new carb piston springs from Moss and tested them against the original springs I now have to see if the original had weakened over time. The old springs turned out to be about 5% stronger than the new, so I'll keep the old and maybe have to put 40W oil in the dashpots.
Ken,
I hope that you have not overlooked the possibility of a poor seal on the top of the dampers. The system is designed for limited air flow. Extra air flow allows the piston to drop faster than desirable.
Charley
 

Graham H

Jedi Warrior
Country flag
Offline
I was going to suggest running a temper wire direct from the battery to the coil to eliminate voltage drop in the circuit

Graham
 
OP
K

Ken H

Senior Member
Country flag
Offline
Ken,
I hope that you have not overlooked the possibility of a poor seal on the top of the dampers. The system is designed for limited air flow. Extra air flow allows the piston to drop faster than desirable.
Charley
Seal is good. New gaskets.
 
OP
K

Ken H

Senior Member
Country flag
Offline
I was going to suggest running a temper wire direct from the battery to the coil to eliminate voltage drop in the circuit

Graham
Good suggestion. After standing on my head working under the dash in 98 deg. weather yesterday, I've decided to run a test wire. I'll do that tomorrow morning, before it gets too hot.
 
OP
K

Ken H

Senior Member
Country flag
Offline
Find the fuse that protects the green wire electrical circuits that are 'hot' ONLY when the ignition key is in the ON/RUN position... and test the voltage upstream of that fuse it should be the full 12 volts..
.That the location, upstream of the fuse is where the coil needs to be fed from.
I think I'll have to do that although I hate modifying the wiring. The current circuit goes through almost every component in the car before reaching the coil. At each connection, I lose a little voltage.
 

poolboy

Yoda
Country flag
Offline
It's not really a modification if you return it to the original configuration like it's shown in the link for the schematics
 
OP
K

Ken H

Senior Member
Country flag
Offline
I was going to suggest running a temper wire direct from the battery to the coil to eliminate voltage drop in the circuit

Graham
I ran a wire directly from the battery to the Pertronix distributor to ensure the distributor got the full 12.4 volts. A wire from the distributor goes to the coil. I started the engine and set the idle to 1200 rpm, which was high enough to observe the ignition spark jumping around as it has before. The Pertronix tech help informed me that if the unit gets 12 volts, it's timing will not drift at steady rpms. I drove the car and still get some minor misfires under a light load at any moderate rpm. I got it to backfire once under full throttle, at low rpm. (3rd gear)

Assuming the Pertronix distributor is functioning well, (a big assumption) the only other factor that could cause early or late sparks at steady rpm would be mechanical. I'm thinking there may be too much end play in the shaft that drives the distributor. I know it's critical and needs to have the correct shims to control endplay. I grabbed the distributor rotor and was able to rotate it 3/16 of an inch measured as shown in the attachment. I know rotors always have some free play, but I don't know how much. I'm hoping one of the followers of this post can tell me if 3/16 is normal or if it's excessive. Perhaps someone can measure their rotor free play and comment.

After receiving a few comments, I'll probably pull the distributor and measure the end play in the shaft and slop in the keyway to determine where the slop in the rotor comes from.
 

Attachments

  • IMG_0953.jpg
    IMG_0953.jpg
    98 KB · Views: 36

poolboy

Yoda
Country flag
Offline
What you may be observing is the mechanical spring advance.
If you can twist the rotor counterclockwise and have it spring back clockwise the same amount when you release it...that's what it is and a normal reaction.
 
OP
K

Ken H

Senior Member
Country flag
Offline
What you may be observing is the mechanical spring advance.
If you can twist the rotor counterclockwise and have it spring back clockwise the same amount when you release it...that's what it is and a normal reaction.
Later this afternoon, it suddenly hit me that I'm stretching the springs on the centrifugal advance. I'm pretty slow to catch on sometimes. I'll have to pull the distributor to see what the play is in the shaft. I know the manual goes into detail talking about end play in the distributor drive shaft so I assume it adversely affects timing.
 
OP
K

Ken H

Senior Member
Country flag
Offline
I've been taking a little vacation from the TR issues while Florida temperatures were breaking records. We had three days of 106F. which is unprecedented. During that time, I kept wondering what could cause my timing to be jumping around and not steady. It seemed like the engine problems were solved except for the distributor. I spoke with Pertronix a few times and ran all the tests they directed me to do and convinced them (and me) the distributor is ok although the timing still jumps around about 3/4 of an inch on the pulley at 1200 and above.

With all other options eliminated, I put my other new coil on the engine for the second or third time and checked the timing. After the switch the timing became much steadier. The timing now jumps between 1/8 and 1/4 of an inch. This is more in the realm of slop in the mechanical end. (wear on timing gear, end play of the distributor drive shaft, and wear of the key in the drive shaft.)

I set the timing to 5 deg btdc at 600 rpm and took the car out for a spin. For the first time in five years, the car ran perfectly!! I could not get a backfire under any conditions. I drove home and did a final adjustment on the carbs (one flat on each) and drove again with equally good results.

In summary, I believe there were several issues with the engine which caused backfire through the carbs and very rich running which the community on this forum helped me to unravel.
  • One carb had a leak in the jet gasket which allowed fuel to bypass the jet and go directly into the engine. New neoprene seals eliminated that leak.
  • Excessive friction on the jet seals caused the jets to not fully retract when the choke was released. The jets stuck about .060 before coming home. New jets with a polished OD reduced the friction allowing the jets to fully come "home" when the choke was released.
  • One major discovery was that the oil I was using in the dashpots was too thin for my driving conditions. Initially I was using 3 in 1 oil, followed by 10W30 and finally 30W oil. I had always read comments that the oil weight was not too important, but I now think it is. I'm going to play with different weights and carb adjustments until I get brown spark plugs.
  • The fuel pump seemed to be underperforming so I put a rebuild kit into it and it seemed to perform better. The old check valves were not completely sealing. I'm not sure if this contributed to the issues, but the effort eliminated that possibility. The fuel filter was also replaced at that time.
  • My original distributor had a leaky diaphragm which was replaced without solving the problem. I also replaced the vacuum line from the carb to the distributor. Still backfired. New points, plugs and condenser did not help. A new timing light combined with a great article on how to diagnose distributor wear issues helped me to decide the distributor had to go. I either needed to rebuild it or buy a rebuilt one. I had the Pertronix distributor here, so I put it on and the backfire issues were not solved!
  • Today, I put on the other coil I have (both coils are new) and the backfire issues finally disappeared.
It's been a very long journey for me and I could not have done it without all of your help. Several issues combined contributed to the problems I was experiencing and your expert guidance helped me to eliminate the problems one by one.

It's probably early to claim victory, but in time I'll see if the plugs turn brown and the exhaust pipe gray. Does anyone know how many hours of driving this should take?

Thanks again to everyone who contributed. I'm forever grateful.

Ken
 

charleyf

Luke Skywalker
Country flag
Offline
Ken,
Apparently the cars are just like many of us. So often it is not just one thing that puts us under the weather, but a combination of factors.
Now put all that stuff behind you and DRIVE ON.
Charley
 
Similar threads
Thread starter Title Forum Replies Date
C 79 Midget Missfire Spridgets 9
C missfire British Motor Corp 3
G TR6 Engine Cutout, Black Smoke, Large Backfire Triumph 7
J Backfire through carbs Austin Healey 3
K Midget backfire at intake side... Spridgets 7
M TR6 1975 TR6 Backfire from Carbs, running Lean - Help! Triumph 9
tinman58 TR2/3/3A Backfire! Triumph 13
T Spitfire Backfire Triumph 1
D Carburetor Backfire on acceleration at low speed Austin Healey 18
H Backfire on deceleration MG 6
D BT7 Tri carb Backfire Austin Healey 2
Jim_Gruber Sputter, miss, backfire, Yuck!!!! Spridgets 27
roofman Spitfire Spitfire backfire, timing or carb? Triumph 12
JPSmit tonight - backfire Spridgets 10
T What causes an engine to backfire? Triumph 15
G Engine Backfire Austin Healey 13
J MGB 1976 mgb backfire MG 5
D MGA mga start and backfire MG 5
R Backfire during decelleration MG 14
R backfire...ect. Austin Healey 50
SilentUnicorn Backfire question Other Cars 11
jerrybny My clunk is gone too and Backfire question Triumph 10
73MidgetLigon mg backfire dcoe Spridgets 31
A TR4/4A TR4A backfire - help please Triumph 15
S Backfire through rear carburator Austin Healey 18
B TR4/4A Tr4A carb. backfire Triumph 3
S Wedge Finally! I figured-out the TR7 backfire problem!!! Triumph 3
S Wedge Help in solving TR7 lift-off backfire Triumph 9
M Help with backfire and smoke Triumph 2

Similar threads

Top