Fuel supply question - Ryobi RCS 3335

[oldnwrinkly]

I know - bin it ........... but it's only got about 20 hours on it although it's now out of warranty. It cost me £40, brand new + warranty (long story) and I bought it as a replacement for my 27 year old Solo 606 firewood saw.

After some initial carb tuning it has always started and run well from cold (still does) but, when hot, if switched off and left for 10-15 minutes it will not start.

The problem seems to be fuel. It has a primer bulb and, when cold, after a couple of pushes the bulb fills and you can feel pressure. When it's hot the bulb goes in and out without any pressure and only ever has a small amount of fuel in it (lots of bubbles). Left to cool down for 45 minutes the primer has pressure and saw starts fine and if not switched off will run out a tank of fuel without any problems.

I have stripped and cleaned the carb and all of the filters are clean - ditto the tank vent. The fuel lines are still flexible and make a tight seal on the carb.

I'm stumped. Anyone come across this kind of thing and found a fix?

 

I know it's only a 'toy' saw but as I said, it starts, runs and cuts well if not pushed too hard and fills my need - also at 68 I don't think I will still be sawing in a couple of years time so if it lasts that long ...............

Edited May 4, 2012 by oldnwrinkly

[GardenKit]

Firstly, welcome to the forum, oldnwrinkly.

 

Secondly, you are right, you should bin it.

 

But in theory it should be fixable, if it was a Stihl, Huskie or similar there would be no question, but the quality of components used in the low end machines often make repairs next to impossible. Dealers in general, wont touch them.

 

Your hot start problem is, I reckon more due to the mixture being a little weak. You should not need to prime on a hot start as the fuel should not have run back, but the primer should still work.

 

If it really does need priming, then I would suspect the carb pump membrane. This has two little flaps which act as an inlet and outlet valve for the impulse operated fuel pump.

 

If these flaps are worn, damaged or degraded in any way the fuel supply will be disturbed.

 

Many of these cheap saws have the carb mounted to the base plate using coarse thread self tapper bolts (not sure if this applies to the Ryobi). The plastic gets 'pulled' into a little lump when the screws are tightened and when the carb is refitted it does not seat well and an air leak can develop. This effects both the mixture, and the strength of the impulse, causing problems such as yours.

 

Hope this helps a little.

[oldnwrinkly]

Thanks for the reply, Gardenkit.

 

Re. the mixture. The 'L' needle is set so the engine is just four stroking a little on tickover. I have tried setting it richer and I have also checked the 'H' setting - this is tuned to max revs and then richened to a slight 'burble' as per usual - but, as I said the saw cuts well (given its puny 33 cc) --- Earlier this week I was logging some fresh felled 25-30" diameter oak and, although slow going, it went fine .... until I switched it off

 

I checked both diaphragms very carefully for punctures and damage and they are both fine. The carb is only a couple of months old (I complained bitterly to Ryobi about the lack of a carb repair kit - there isn't one yet for this saw - and they sent me a new carb !!) so the diaphragms should be good.

 

The carb is mounted to the cylinder via a typical plastic spacer which transferes the engine pulses from the bottom of the engine manifold to the top of the carb. The plastic looks to be of reasonable quality and does not show any deformation.

 

I removed the carb again last night and did notice that the (very low quality) gasket between the carb and spacer was deforming and had reduced the depth of the pulse transfer channel quite a bit so I have made a new one. I will re-assemble it all later today and check it out - probably will need to re-tune the carb settings.

 

This is the first time I have encountered a bulb primer system but it looks simple and straightforward and that's why I am puzzled at the way the saw is behaving.

[Adamam]

Probably not very helpful, but I've heard numerous stories of people buying Ryobi gear, it breaking almost immediately, and Ryobi being ultra-effective/generous in terms of repair/replacement.

 

My understanding is that Ryobi purchases are usually made primarily with after-sale service in mind.

 

Have you approached them with your problem?

[Les Cork]

Hi

this is classic vapor lock, your saw runs fine from cold and then when hot doesn't like starting, the fuel mix is vaporising before the cylinder and forming gas lock.

The reason this happens is that when you run the saw the flywheel fan flows cool air around the cylinder optimising running temperature, when you stop the temperature goes up hence why the fuel left in the carb gets heated up to vapor.

Ways to get around this are

Add fuel additive to your petrol prior to adding the oil mix

ensure you use a quality two stroke oil and be generous not mean

buy the better unleaded fuel

keep your saw clean use an airline to blow out all the sawdust and chippings from around the cylinder head etc

try starting the saw with the throttle full on [apply chain brake first] this can be done on the ground

Keep chain sharp, depth guages correct and tensioned and ensure the chain oil is getting thru to lubricate as this is another heat source if wrong.

Several years back this was a problem for a lot of manufacturers.

 

Good luck and be safe

[oldnwrinkly]

Les,

 

Thanks.

 

Yes, a vapour lock seems to be the problem but I couldn't see a way around it. I assumed that the fuel was vaporising in the carb but, as it is fitted with a bulb primer I thought using this might have forced fuel back into the carb. Obviously the lock is blocking this route also.

 

As supplied, the 3335 did not have a throttle lock but did have a blanking plug over a hole in the handle where one would be and the trigger 'safe' lever also was designed to accommodate a pin/button so I turned one up from SS. I always did a hot start on the Solo with the throttle locked on full. However, even trying to start the 3335 with the throttle locked open doesn't work.

 

All of the other points you mention are within my normal operating procedure/care and maintenance routine ( e.g. I run a 40;1 mix as opposed to the recommended 50:1).

 

I am hoping that fixing the gasket problem I mentioned may help - if the pulse was weakened due to the transfer channel being partially restricted this would result in low efficiency pumping, yes?

I forgot to mention that this hot start problem is relatively recent. I didn't notice it when the saw was new.

[GardenKit]

Vapourisation is indeed a possibilty, but I don't see how it will affect the operation of the primer, which draws fuel from the tank via the carb, thru the bulb and back to the tank.

 

Another thing to check is the plug gap. Wide gaps cause hot start issues.

[pro bros]

i am no tech buff and you seem well clued up but let me add my opinion on the matter i agree with garden kit regarding spark plug i also once went to purchase a low cost saw and was told that because of the crank being 2 piece? it would go out of time when hot and give problems starting etc this could have been a sales pitch but seems plausable

[felixthelogchopper]

Les,

 

Thanks.

 

Yes, a vapour lock seems to be the problem but I couldn't see a way around it. I assumed that the fuel was vaporising in the carb but, as it is fitted with a bulb primer I thought using this might have forced fuel back into the carb. Obviously the lock is blocking this route also.

 

As supplied, the 3335 did not have a throttle lock but did have a blanking plug over a hole in the handle where one would be and the trigger 'safe' lever also was designed to accommodate a pin/button so I turned one up from SS. I always did a hot start on the Solo with the throttle locked on full. However, even trying to start the 3335 with the throttle locked open doesn't work.

 

All of the other points you mention are within my normal operating procedure/care and maintenance routine ( e.g. I run a 40;1 mix as opposed to the recommended 50:1).

 

I am hoping that fixing the gasket problem I mentioned may help - if the pulse was weakened due to the transfer channel being partially restricted this would result in low efficiency pumping, yes?

I forgot to mention that this hot start problem is relatively recent. I didn't notice it when the saw was new.

 

To me, that suggests that Les's comment about overheating could be the problem. Have you blown it out with an airline?

[oldnwrinkly]

With the engine cover off you have a good view of the cylinder and easy access for cleaning so I regularly brush and blow out any fine sawdust deposits from the fins and the rest of the cooling air path.

As I noted, the mixture appears to be OK (maybe even a little on the rich side ?) so all in all I don't think it's a case of overheating during normal running. The plug colour looks about right - dark tan so not a weak mixture.

 

At the moment I am still convinced that the problem lies in the fuel system - I just cannot understand why the priming system loses pressure when the saw is hot - but, just in case I am wrong I have checked the plug. The gap is spot on (0.025") and there is a good spark when the engine is hot - whether it is still timed correctly may be another story. A spare plug made no difference.

 

The operating instructions do say that the primer should be operated for a hot start and to just omit the choke operation, as you would expect.

 

After fitting the new gasket the carb did need re-tuning - the mixture was a little too rich but after adjustment the saw still would not start when hot.

 

Thanks for all the replies thus far.

You might wonder why I am persevering with this thing - you could say that it's earned it's money with two or so years of use and could be binned - but it annoys me when I can't find a reason for what appears to be a simple problem. Apart from that, generally the saw is in very good condition, nearer to just 'run-in' than worn out and, probably because I grew up in a time when stuff like this was expensive and scarce, it seems a waste of resources to throw it away because of a niggley fault - after all, it does start and run well (mostly )