Datsun Roadster Forum-311s.org

Hey guys,
I picked up a 1967.5 1600 a couple weeks ago, and it ran great for a while. Bad news is recently it has started hesitating and bogging durring acceleration. This usually only happens when accelerating or when going up a hill, and it seems to maintain speed fairly smoothly. Also, the engine only revs to about 3800 rpm, then it starts some weak backfiring through the carbs and won't rev any faster.
At first I thought it might be the carbs, but after reading some posts on this fantasic forum, I now suspect it's the timing. I already checked the fuel filter, points, plugs, plug wires and topped up the ATF in the carbs and that all seems okay. I do have about a quarter inch of free-play in the rotor on the distributer, could this be a problem?
I'm going to buy a timing light tonight and make sure the timing is set to 16 degrees, but I have never done this before and any suggestions would be most welcome. Any other ideas on what might be wrong?
Thanks!

After some investigation I'm seriously considering a Gary Boone electronic dizzy. To revamp my current set up I'd probably spend almost $130 on parts, so the Boone unit is not far out of reach. good idea you think

That sounds almost exactly like what was happening after I rebuilt my carbs. I tore my hair out, checking and rechecking my carbs. It turned out that my rebuild was fine, but somehow my timing was way off. By like 10 degrees. I would defineatly start by checking the timing.

Checking the timing is easy, red clip to the positive battery post, black to ground, and the last one should loop to 1st spark plug wire towards the front. Then pull the trigger and aim it at the lower pulley. You should see a pointer and a small mark on the harmonic balancer. My car doesn't have a gauge mounted on the block, so I had to use an advanced timing light, which is easier anyway, though a little more expensive. When I set the advance on the timing light to 16, the pointer and the mark should show at the same time, during the pulse of light. It's kinda like a strobe light.

In terms of the Gary Boone Dizzy, I have heard nothing but great things by everybody who has one, and am planning on getting one myself soon.

Good luck.

Hey Joe,
Thanks for the advice. I bought a timing light yesterday and checked it - much easier than I thought it would be. Turns out the timing was off by about 8 degrees. I adjusted to 16 degrees BTDC and the car runs much much smoother. I still can't get it to rev past about 4200 or 4500 rpm, and it backfires out the carbs a little bit when running that high. Could this be due to the vacuum advance unit? The PO said it was bad, and I have ordered a new part, but it probably won't be here for 2 or 3 weeks. Maybe the carbs need to be adjusted some?
Thanks

A bad vacuum advance could defineatly do what you are describing. You could try the simple exercise of sucking on the vaccum tube and seeing if it moves the advance lever. If your thinking of getting the Gary Boone Dizzy, it might come sooner than 3 weeks, and the hardest aprt about installing it is probably setting the timing.

My experience with the carbs is that if they are running good at 1000 and 3000 RPM's, than they should be okay at higher rev's to. Adjusting them is pretty easy also, once you learn how, which isn't as easy.

Other people on here have far more experience than I do with these cars, but trouble shooting can be pretty hard when your not hands on. I'm sure you'll get more suggestions, but my favorite is to only try to do one thing at a time, rather than go and adjust the carbs, reset the timing, change the spark plugs and replace the fuel pump, then try it out.

Good luck,

That 1/4'" of play you have in the rotor is not a good thing. The bushings are probably pretty well worn. A Gary Boone EI dizzy is definitely the way to go. You can buy a stock rebuilt dizzy for around $125.00 but for $100.00 dollar more you get a rock solid peformer with the EI conversion. The SU carbs when they are dialed in should need no adjustment at all. They are great carbs. Good luck!

Steve

Here's another testimonial for Gary's Dizzy and I'll throw in another for Keith William's carbs. My '69 2000 starts easily, pulls strong to red-line and idles at 600 rpm. Money well spent. Pat Mahoney

Yes, I will give Keith my positive vote for rebuilding SUs as well. He has done several sets for me and they were pefect. No problems at all. I believe he is a bit cheaper than the competition as well. You just cannot be in a big hurry as he done them part time.

Steve

Re: backfiring, check your valves. If they're adjusted too tight they won't close all the way allowing backfire through the carbs. It'll also make the car run poorly. The EI distributor is certainly a good thing but it'll rev past 4500rpm if a stock points distributor is in good working order.

Two Cents,

If the problem has occured rather quickly, and you said you have good idle and non load performance. I would check fuel volume and pressure at the speed / condition which the problem occurs. You may have a problem with your fuel pump, fuel line or tank pick-up. You said the fuel filter is good, but is fuel getting to the carbs during accel ? Always check the simple stuff first. Back firing is also caused by a lean condition in the carbs. The ignition timing may also be a culprit, but it usually comes about slowly, unless you have the major malfuntion. The vacuum advance unit on your dist is only for part throttle anyway, the full timing advance is mechnical. Is the vacuum line from the dist. going to a ported vacuum source ? If the vacuum unit fails for what ever reason, you will have poor throttle response , but good idle and full throttle performance, it will just take longer to get there.
Now onto full spark voltage, if your ignition is getting weak in its old age, your will lose voltage when you need it most, heavy accel and hills, this will cause very poor performance and back firing due to plug fouling. Start looking at condition of the ignition system and think about a new coil. EI system from Gary Boone might be something to look at if you want trouble free ignition system.

Again this is all simple stuff and can be worked through in a hour of diag.

My Two cents, and a bit more
JC

I agree, you could be suffering from fuel starvation. If your float bowls aren't ajusted correctly, you will suck them dry and end up with an engine that pings, and doesn't pull anymore past a certain RPM. You can buy SU rebuild kits that include new floats and gaskets and possibly new float jets for fairly cheap. An easy way to tell if your going lean is to take it out on a road with litte traffic and run it till it starts being wierd then put the clutch in and turn it off and coast to a stop. Check the plugs and if they are white you might have found your problem.

Good luck
Will

I also recently acquired a Roadster that did the same thing. Ran great for about 50 miles and then would bog or sound like it was on 2 cylinders. After removing the carbs, taking them apart, replacing the floats (mine were all dented and soldered!) cleaning the nozzles, and especially the SMALL SCREENS were the fuel enters through the tower on each carb.

There is a bolt (about 14mm) where the fuel enters the float chamber that has a hole in it that is then filtered by the small screens. This was where the stoppage was. There was so much sludge from the gas tank that was never cleaned (another post entirely).

I bolted the carbs back on and have had no fuel problems since. I also am running 2 fuel filters now just to be sure that sludge is not gettin to the carbs.

BTW, screw the bottom nut on the carbs all the way in and then only 2 turns out. Adjust the throttle stop screws when the carbs are off the carb. Loof down the throat and adjust the screw to open just so a little light peeks through.

Ron

Thanks for all the replies guys - Roadster owners are definitly a dedicated group!
As for the bogging, adjusting the timing helped a great deal. The carbs were rebuilt several months ago so they are *probably* okay. I poked around the dizzy this weekend to see what I could, and it turns out the vacuum tube from the carb to the advance unit is leaking. The end broke off at some point, and instead of replacing the whole tube the PO put a glob of silicone sealent on the end to "fix" the vacuum leak The silicone is cracked by now, so I know the vacuum advance is currently not functioning.
I've placed an order to get a new tube, and I'm also thinking this vacuum leak could be contributing to the problems at high RPM. When the vacuum draw is heavy at the carbs (high RPM) it would suck extra air in through the crack in the line causing a lean condition correct? Hopefully a new line and some grease on the dizzy will fix the problem, but sooner or later I will get a GB electric dizzy.

On a positive note though, my turn signals worked for about 30 seconds this weekend - they have not flashed since I bought the car. This tells me the problem is a loose wire somewhere and not the ($$$) turn signal switch. I'll work on this and check the valve clearance next weekend.