volvo B20 dual stromberg carbs back fire when reved

[johnmorgan]

I just got my first boat, and the motor ran and idled good but when I rev it up it back fires out the carbs. Gas and some times flames come out. it idles fine i did the timing idles even better now but cant even touch the throttle with out it back firing. any help would be good . thank you all. i looked online for other motors problems but they all have carbs facing up, not out, like my motor. could this be a car motor it is cooled with a HX. thanks again.

 

[captmello]

Re: volvo B20 dual stromberg carbs back fire when reved

I was thinking timing as well. Have you changed out the points and condenser yet? I'd swap those out, set the points with a dwell meter, and reset the timing.

Good luck!

 

[PiratePast40]

Re: volvo B20 dual stromberg carbs back fire when reved

Take a closer look at the engine. The B20 (AQ130) is a raw water cooled engine. The earlier models did have Zenith-Stromberg side draft carbs, but none were originally equipped with a sealed cooling system. If an AQ130, it has an oil cooler mounted under the oil filter. That is certainly a heat exchanger but not for a closed cooling system. Take a closer look at the tag either just forward of the starter or on the port side of the flywheel cover so you can make sure of the engine type.

If the boat is new to you and you don't know the maintenance history, a good tuneup is usually in order. If initial timing is good, you still need to check timing advance to make sure it's working. Firing order for an AQ130 is 1-3-4-2 and rotation is counter clockwise so check that as well. A cracked or wet distributor cap can cause crossfiring and backfiring as well.

If things aren't clearing up after a tuneup, and distributor advance is working correctly, might start checking valve springs and do compression and leakdown tests.

Like the captain mentioned, I'd really be inclined to verify the ignition and timing before digging into the carbs but you really need to verify the engine type first. If an overhead cam engine, it has a timing belt, and that may be an issue. I believe the AQ120 overhead cam engine had twin strombergs.

 

[johnmorgan]

Re: volvo B20 dual stromberg carbs back fire when reved

i went and looked, there is no aq120 or anything other than a couple of different numbers just beside volvo b20 and just above the starter. the guy i bought the off boat said it used to be cooled with raw water, but he put a hx to cool it with fresh water ,and he put a custom pump to cool the hx with raw water. i noticed that where you clip the cap down there is a chunk of the cap missing so there is a hole in the side of the cap i didnt know that it would matter? do you think i should get an electric ignition or try the caps. I have never heard of a dwell meter and wouldnt know how to use it if i had it

 

[PiratePast40]

Re: volvo B20 dual stromberg carbs back fire when reved

A picture would go a long way toward resolving the issue of which engine you have. Would also give a bit of insight on the cooling system. A modified cooling system is a bit of a fly in the ointment but sounds like a fun challenge.

If you're talking about the distributor cap having a chunk out of it, then yes, that could be a problem. Not to make light of your knowledge level, but some of the more advanced members here might be saying something like "here's your sign". Just roll with it and have a chuckle about it later.

I have the Hot Spark brand ignition module with their 3 ohm coil. It's worked great for me. You'll also need to bypass the resister but that's no big deal. I'd advise to use it at your own risk and be aware that if you swap leads and reverse polarity, you'll be sending another $49.95 to them! To help make your decision, a new condenser alone will run $27 to $49 depending on which distributor you have. For me, it was a no brainer and I haven't looked back.

Short answer - yes, get the ignition system working correctly and see what that does for you.

 

[johnmorgan]

Re: volvo B20 dual stromberg carbs back fire when reved

here r some pictures

 

[johnmorgan]

Re: volvo B20 dual stromberg carbs back fire when reved

my knowledge is all coming from being a fix it your self guy,and this forum. I am only twenty one and this is my first boat and first volvo cool motors though. can't wait to get this boat out on the water payday is on friday and my birthday is on tue hope to be running by then. thanks for your help every one

 

[captmello]

Re: volvo B20 dual stromberg carbs back fire when reved

Ya, thats quite the DIY cooling system. i hope it works for you. A cracked distributer cap is going to cause problems. If you can't do a tune up yourself, get someone to help. With an out of tune, unknown engine, you're just making it harder to find the issues and raising your chances of breaking down on the water.

 

[sqbtr]

Re: volvo B20 dual stromberg carbs back fire when reved

Looking at the pictures I woud say that is an automotive engine

No raw water pump provision on timing cover and no spark arrestor.

Those carbs require oil to dampen the enrichment jet, backfires were common and would sometimes blow the diaphragm.

Please check marine requirements for ignitition protected components before endangering yourself and others.

 

[PiratePast40]

Re: volvo B20 dual stromberg carbs back fire when reved

Someone sure spent a lot of time tinkering to build that arrangement and it leaves you with a ton of unknowns. I agree with sqbtr that it's an automotive engine. No raw water pump opening on the timing gear cover is the giveaway plus the automotive circ water pump is still installed. The automotive thermostat cover is installed as well. There is a marine exhaust manifold installed but you have no idea if the alternater and starter are marine rated. Might be and might not be.

There isn't a ton of difference between the basic marine and automotive versions. Raw water pump mount and steel timing gears in the marine version are the main differences other than the spark protected electrical components, exhaust system, cooling system, and carbs. If you decide to keep it, there may be some hope for the engine.

For me, the first order of business would be to determine if it's safe enough to run in an enclosed space. Do you have the spark arrestors for the carbs? Or at least an air intake box?

We can play guessing games about why someone would do that and how to keep it running but it really boils down to a decision to return it to a safe and reliable engine or continue working on Frankenstein.

EDIT: If you're looking for distributor parts, you'll need to find the part number of the distributor. It's either stamped on the housing or on a brass plaque. You only need the last 3 digits. 010, 011, or in some cases 012. From there you can determine which cap, condenser and points. The caps are definately different so you need to be sure. The distributor shown in your pictures may be an automotive style. The reason I say that is that on the marine versions, the pigtail from the condenser to the distributer is integral to the condenser and connector. On yours, it's a separate jumper wire. For points, from what I'm reading, any of the one piece point sets will work in the distributors that use one piece points. If you can find someone willing to help you do the tuneup and set the dwell and timing, then I'll send you some links to the ignition tuneup parts. Just be aware that you may be departing from marine rated components and you should only do this to find out if the engine will stay running long enough for you to determine it's condition.

 

[johnmorgan]

Re: volvo B20 dual stromberg carbs back fire when reved

I was hoping it was a marine engine. dang oh well, i know i need a marine alternator for sure then, i have a intake box though i dont know how much it would help. ok so i should just try and get it running by changing the points, then change it to a marine engine. i know that i have a marine starter because it is new and there is a bill of sale for it. ok guys i am going to get to work on this, if in fact i get this motor running what are the marine parts i need to be safe. for now thank you all for the great help. cheers john

 

[PiratePast40]

Re: volvo B20 dual stromberg carbs back fire when reved

Get a manual for the engine. You really can't do much at all if you dont know how things work. Cap, rotor, and points are a good start.

You can take the alternator to a rebuild shop and they can tell you if it is in fact a marine alternator. May even be able to add the screens if possible and needed for that type.

The carbs should have a spark arrestor on the inlet side. That would be a screen that looks like an air filter. I believe that on those carbs, the would be flat and square - one for each carb inlet.

I didn't see a bilge blower suction hose sticking down into the bilge. The purpose is to ventilate any gasses and these are heavier than air so sink to the lower areas. Coast Guard regs call for the suction hose to be in the lower 1/3rd of the engine compartment but common sense tells us that it should also be above the expected water level in the bilge. You may also have another air outlet that doesn't depend on the blower but flows out naturally when running at speed. Those are some of the basics.

 

[johnmorgan]

Re: volvo B20 dual stromberg carbs back fire when reved

turns out there was no oil in the carbs. i put oil in and it revs good now. ordered new points but canceled that, because i went for a burn, and at high rpm smoke started coming off the exhaust manifolds until i went to about 2500 rpm. I am no expert but smoke coming from there is usally not good. so i just ran home really slow. also my alternator is marine luckly three hundred for a new one. i could not find spark arresters anywhere so just put the old cover on for now and left the motor open so no gases could build up. good thing you guys mentiond that because i would have never know about those blowers. thank you. should i start a new thread about the smoke coming off the exhaust manifold or can some one help me.

 

[sqbtr]

Re: volvo B20 dual stromberg carbs back fire when reved

You have a montage of parts there. And without seeing the cooling system layout, and not quite understanding the circulation and raw pump.
The raw water pump would be my first look. Check the impeller. What was the engine temperature?

 

[PiratePast40]

Re: volvo B20 dual stromberg carbs back fire when reved

The location you describe is the exhaust port area for cylinders #2 & 3. It's possible that you have an exhaust gasket leak at that area. But without knowing temperatures, it's hard to say. The top of the exhaust manifold should be a little warm but not hot. The front cover and the bottom are where you'll be seeing the highest temps so those would be the areas to check.

I see that there's a strainer of some sort installed, would be a good idea to check that but we're really in a guessing game right now until you have more information.

 

[johnmorgan]

Re: volvo B20 dual stromberg carbs back fire when reved

I dont have an accurate temp gauge but the gauge with the green and red read in quarter range.I did start a new thread for this because its the rules

 

[sqbtr]

Re: volvo B20 dual stromberg carbs back fire when reved

Looks like we are sticking with this thread. Capt and pirate are up to speed on these powerplants. You have a bastard child and more pics would be nice, especially of how the feed water is delivered.

Normally the oil cooler is first in line and the exhaust manifold is next. I don't see the normal cooling tubes from each exhaust port. Get a good pic of the starboard side of the engine and maybe we can figure out the flow.

 

[PiratePast40]

Re: volvo B20 dual stromberg carbs back fire when reved

I dont have an accurate temp gauge but the gauge with the green and red read in quarter range.I did start a new thread for this because its the rules

The temps I was referring to are low enough for you to feel with your hand. Top of the thermostat housing and top, forward portion of the exhaust manifold are normally relatively cool so you can check by hand. Higher temps will be just below the thermostat housing on the head (where the temp sender is located) and the lower portions of the exhaust manifold. The idea here is to see if the engine is actually overheating or if it's a gasket or piping leak somewhere. This is also a perfect excuse to buy one of the new remote temp guns with the laser pointer .

 

[johnmorgan]

Re: volvo B20 dual stromberg carbs back fire when reved

yeah I need one of those temp gauges to get an accurate reading i wil get some pictures and post them on my new thread.