Aircooled 1600 Popping at high rpm

[ecthemc]

Hello everyone- I'm new to the VW world and inexperienced with working on these engines.

I purchased a aircooled 1600 powered sandrail and have some kinks to work out- hopefully one or two of you veterans here can help me..

When engine is in neutral, not moving, I can rev the engine out just fine.. But when its underload (driving) and I get high in the RPMS the engine pops. Thus not allowing me to achieve high rpm, I can "throttle through it" but it really doesn't give me any power. I've changed the 009 Distributor cap, spark plug wires and im running NGK 5' Spark Plugs ( repaced recently had 6's 3&4 had build up.. specifically 3 was pretty bad) , I checked the Intake/carb for leaks , and even checked the fuel filter. My motor has a mechanical fuel pump and a single double port carb... What I haven't done yet (but been researching so I make sure I do right) is adjusting/checking the valves, and the timing I will do tomorrow. I also haven't taken the carb apart (it has a snorkel) but have disconnected the snorkel.

Any suggestions?


https://www.youtube.com/watch?v=QVc_AfyCHkQ&list=WL&index=27

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[Brian]

Popping through the carb or the exhaust?

Welcome to the samba, look over these videos to learn the basics of the VW engine.

Valves:
https://www.youtube.com/watch?v=EpH7VftH3_I
https://www.youtube.com/watch?v=vQ9ccGXtZL0

Timing:
https://www.youtube.com/watch?v=xm4OmiVH2J0
https://www.youtube.com/watch?v=cIrA4iWkhbE
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'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper

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[ecthemc]

I'm fairly certain through the carb... sounds like carb

(only way to hear it is while the vehicle is driving under load, sitting in neutral revving the motor won't trigger the popping).

thanks for the videos

[Brian]

I'm pretty sure it's the valves being too tight. A good cold valve job should help out.
_________________
Wash your hands

'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper

Only losers litter

[Dale M.]

If its popping back through carbs it could be its going to lean at high rpms.... What carb and what jetting?...

Dale
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"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[anobii]

Backfire (popping through the intake side) is usually caused by a lean condition. If does it at a certain rpm, its likely a fuel feed problem like a partially clogged filter or pick up tube/sock in the tank, weak fuel pump, pinched line, incorrect float setting, too tight intake valve lash or a possible vacuum leak. Pulling too much timing advance at high rpm can cause it too.
If its back firing at wide open throttle or at certain throttle positions, you could have a partially restricted jet or circuit, incorrect jetting, accelerator pump issue.

Afterfire (popping through the exaust side) is usually cause by excessive fuel or rich mixture, too tight exhaust valves, or not enough timing advance. Generally afterfire won't cause an excessive amount of power loss but over time it will cause other issues.


Based on you being able to "throttle through" it sounds like you can feather the throttle to get more rpm. By doing so your cycling the accelerator pump in the carb and adding fuel.
I would start with your fuel system, before jumping into valve lash adjustment, and mechanical problems.

Start at the tank. Does it have a screen/sock in the bottom is it clogged? Does the take have a vent? Could be vacuum locking at higher engine speeds.

Next, the fuel line from the tank to the fuel pump. Are there any kinks? Is there a pre filter before the pump? Are the rubber lines soft or hard? Hardened rubber lines can crack through, wont leak but will suck air that will cavitate the pump. Clamps on rubber lines tight? Rusty pinholes in metal lines?

Then, fuel pump. Its hard to tell if its pumping good volume at higher rpm. If its cheap enough, just replace it with a brand new one. Check the fuel filter if it has one after the pump. Kinked lines after the pump?

After all that then take a look at the carb. Probably need to pull it off and tear it down and clean it really good. Check jet sizes, accel pump, basically blueprint the carb so you eliminate variables.

If the fuel system is 100% and since you've already done ignition, then get timing spot on. Then do valve adjustment.

[ecthemc]

Holy moly thanks for all the feedback..

The rail is @ my shop so i'm working on it intermittently through the day..

I'll slowly go over everything that was suggested..

At the moment i'm waiting for some gaskets as I just did a valve adjustment and there was waaaay too much home made gasket maker to justify putting the covers back on how they were.. Secondly I just found a Exhaust leak so I had to order intake/exhaust gaskets (they all came in a kit) - I'm going to go ahead and put them all on ( why not?)

I got a bit bored of the technical shit and through my speakers on Noam NU4 or something, badass little setup they sell for around $200-

https://clips.twitch.tv/CloudyTenderGrouseMikeHogu

[BFB]

not to change the subject but what can you tell me about those rear tires? seen pics of one's like that on vintage buggy but not anything new

[dustymojave]

Armstrong used to make tires like that but without the crossways grooves. Many buggy folks would then cut their own cross grooves how they wanted them.

Such tires may still be available for agricultural use.
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Richard
Offroading VW based cars since 1965
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Retired from building Bajas, Fiberglass Buggies and Rails in the Mojave Desert. Also Sprints & Midgets, Dry Lakes, Road Race cars. All types New and Vintage
SoCalBajas Member
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