Ace Posted April 17, 2021 Share Posted April 17, 2021 Our ride on Ransome club mower with a MAG engine has a running issue. Starts and runs great for about 20 minutes then loses power as though the timing/compression/mixture changes. Will restart then just tickover but as soon as you try to increase the revs coughs, splutters and occasionally appears to spit back through the carb. Fuel flow from the tank is excellent and we have changed the plug and carb. Compression seems to be still there when pulling the starter when hot but there will be considerable mechanical drag. Let it stand for 30 mins and then it will run for say another 10 min then develop the same problem and stop. Any thoughts? Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted April 17, 2021 Share Posted April 17, 2021 Don't know that engine but will do some research.... Does a club member have a red neon plug cap that flashes when HT passed thru it, and does the engine have CB points ? If fuel direct all ok and compression good, then ignition problem, heat related, coil or condenser/capacitor related. It sounds a bit clattety, cooling system ok ? and fuel cap vent ? What model engine? Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted April 17, 2021 Share Posted April 17, 2021 I assume that switch on the bars is a ign kill sw ? Is that a "make" contact to run and a "break" contact to stop ? Two wires joined to run, contact broken to stop ? Any problems with that switch ? 4t side valve ...what model ? Quote Link to comment Share on other sites More sharing options...
Ace Posted April 17, 2021 Author Share Posted April 17, 2021 Hi Rich, Many questions I don't know the answer too as yet but will try to find out? Does a club member have a red neon plug cap that flashes when HT passed thru it, I don't believe so and does the engine have CB points ? ? - looking for a manual. If fuel direct all ok and compression good, then ignition problem, heat related, coil or condenser/capacitor related. It sounds a bit clattety, That's the centrifugal clutch catching just before biting as revs rise cooling system ok ? Appears to be, no debris and can feel air from flywheel fan over head and fuel cap vent ? Clear What model engine? Will need to verify. I assume that switch on the bars is a ign kill sw ? Yes Is that a "make" contact to run and a "break" contact to stop ? Not sure Two wires joined to run, contact broken to stop ? as above Any problems with that switch ? Not that we can tell, won't start when switched to red and kills immediately anytime. 4t side valve ...what model ? Need to check but found a manual covering several one of which is ours. 36" ransomes mastiff Our thoughts were heat was affecting something as after 20 mins running fault appears never sooner and after 15 min rest will run properly for another 10 min -etc. etc. However it does spark bright blue when resting but as to timed correctly? Manual attached. Well try and find the answers to above and come back. Thanks, David 346071950_MAG1023103510401045SRLmanuel.pdf Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 17, 2021 Share Posted April 17, 2021 Check that the tank vent is clear - probably in the cap. Take the cap off when it starts playing up and it clears then that would confirm the cause. 1 Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted April 17, 2021 Share Posted April 17, 2021 Possible overheating, have the valve gaps been checked? Quote Link to comment Share on other sites More sharing options...
Ace Posted April 17, 2021 Author Share Posted April 17, 2021 MH - and fuel cap vent ? Clear AG - have the valve gaps been checked? Yes but only when cold as inspection cover requires the exhaust removing. We did think of the inlet valve sticking slightly open in guide when hot. Sometime next week we should be able to borrow a compression tester to compare cold and hot/fault. Quote Link to comment Share on other sites More sharing options...
Geoff S Posted April 17, 2021 Share Posted April 17, 2021 (edited) If you've been mowing in cold, damp conditions, the carb could be icing up. It certainly sounds like fuel starvation which could have several causes and could be something as simple as a bit of floating debris in the tank or feed to the carb. Edited April 17, 2021 by Geoff S Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 17, 2021 Share Posted April 17, 2021 I was literally just about to suggest the same thing! Has it started doing this since the after market air cleaner was fitted - the original one may have been designed to draw warm air into the carb. Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted April 18, 2021 Share Posted April 18, 2021 (edited) Years ago we had a Ford Escort that did exactly the same, we took the carb apart many times as it was obviously fuel starvation, on the 5th or 6th strip down we found a bit of fluff lodged in a nook (a dead end left by the drilling of the fuel feed), this was obviously moving in use and then blocking the fuel flow, stop the flow and it floated back into it's recess. After the piece of fluff fell out we never had this problem again. I won't say the car ran faultlessly as it didn't, we ended up scrapping it when the drivers seat was in danger of falling through the floor! The other thought, is it a magneto ignition? if so that could be overheating. Edited April 18, 2021 by Frank Skilbeck Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted April 18, 2021 Share Posted April 18, 2021 When it conks out, ie won't rev beyond a certain revs, establish if it has lost HT, use a red neon plug cap that will flash when HT passed thru, it can be fitted and used when the engine is running, it conks and no flashes at that time means...... It could be a but of debris in the carb....being sucked into a jet etc., but that would tend to be random... Establish HT when at working temperature, it may produce HT at the plug in atmosphere, but does it loose HT when warm and at throttle open ! A flash of inspiration needed me thinks ? The red neons don't cost much and really save hair loss ! Quote Link to comment Share on other sites More sharing options...
Ace Posted April 18, 2021 Author Share Posted April 18, 2021 Thanks guys. Only used when grass is dry and therefore reasonably warm ! Did the same thing even with the old carb and filter. Carb/fueling was our first thought hence the clean first then a change. Tried pressurising and even lowering by blowing and sucking into the tank - no effect. Starts easily and as the fault only occurs after 20 min ish running we believe it is heat build up related. Something expanding or breaking down when hot. Particularly as it needs to rest/cool for a good 10 min possibly more before it works again. The longer the rest the longer it will work before stopping again. Whats confusing is that it will start/idle just not throttle up. Can't help think it sounds wheezy with what sounds like pops coming back through the carb as though its blowing back through the inlet valve. Stuck open or timing changed - but it will start/idle. We will see if the compression tester next week helps identify or eliminate anything. Quote Link to comment Share on other sites More sharing options...
Ace Posted April 18, 2021 Author Share Posted April 18, 2021 Rich - fault occurs when running ie fine then wheeze's/pops then stops. However if you immediately reduce to idle it will stay running, just won't then throttle up so we conclude spark ok. If compression test is ok then a red neon will be next as we are then grasping at straws. Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted April 18, 2021 Share Posted April 18, 2021 How is the plug colour, can you post a picture of the plug firing end ? It's a sv 4t so probably has not grown "whiskers" but it does happen very very occasionally. Clean carb again perhaps ? You sure the fuel tap is not vibrating closed, or semi closed reducing fuel flow ? Anyways, you need to rule out something, the easiest being HT with a red neon plug cap, it fits inline with HT lead and plug, giving a quick visual indication of HT and relative strength, but you may need to give it some shade if using outside. It is a real world engine running test but of kit. I use them lots for petrol engine problem diagnosis. Well worth the money and stops you getting bald and dizzy. Have fun ! Quote Link to comment Share on other sites More sharing options...
BackinBlack Posted April 18, 2021 Share Posted April 18, 2021 You could try talking to these people: Meetens engines Quote Link to comment Share on other sites More sharing options...
wingcoax Posted April 18, 2021 Share Posted April 18, 2021 Just an idea, Does it have a choke? Is it manual or auto? Is it moving on whilst running? That would produce that effect. Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted April 18, 2021 Share Posted April 18, 2021 Has anyone had the carb off for 'servicing' before this problem began? Quote Link to comment Share on other sites More sharing options...
Robert Cracknell Posted April 19, 2021 Share Posted April 19, 2021 The Ransomes range of mowers are still manufactured at their original site in Ipswich - maybe someone there could help...? They are still the favourite mower for many golf/tennis/bowls clubs so if you have one of these near you it might be that you have someone with experience you could tap in to. Failing that contact them direct - https://www.jacobsen.com/ Quote Link to comment Share on other sites More sharing options...
Ace Posted April 19, 2021 Author Share Posted April 19, 2021 Rich - plug colour, light covering of black sooty, probably when we tried opening the choke which just caused it to bog, no whiskers. Carb changed same fault b4 and after. Friction tap pointing down for on, no movement. HT neon cap ordered. B in B - Thanks may do if still stuck. Wincox - manual, no movement but if moved when hot chokes engine. Cuban - Carb changed same fault b4 and after replacement. Robert C - we have the original manual and have also downloaded the parts and Op instructions from your link. Once Neon tester arrives we will try it and the compression tester to see if the results point us in a specific direction. Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted April 19, 2021 Share Posted April 19, 2021 Can't see the manual and parts download images.... Does it have CB points ? If yes, how is the gap ? Can the points be seen when engine running thru a flywheel window ? Much arcing going on, bright arcing, and points very white ? I assume the wiring to the kill switch is all good.... Quote Link to comment Share on other sites More sharing options...
Ace Posted April 19, 2021 Author Share Posted April 19, 2021 Rich - Parts, manual attached. Does it have CB points ? Mag with points I believe although not visible through the flywheel without removing recoil starter/mesh cast cover. Look later in the week. Any problems with that switch ? Not that we can tell, won't start when switched to red and kills immediately anytime. HT and compression tests later in the week. Quote Link to comment Share on other sites More sharing options...
Ace Posted April 19, 2021 Author Share Posted April 19, 2021 Might help if I actually attached the parts/manual ? 1123117649_Mastiffoperatorinstructions.pdf Mastiff parts list.pdf Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted April 19, 2021 Share Posted April 19, 2021 Great, my internet phone will not open those files... Quote Link to comment Share on other sites More sharing options...
Brian Lambert Posted April 19, 2021 Share Posted April 19, 2021 Just a thought, is there a capacitor (condenser) across the points? they can fail shorted when hot. 1 Quote Link to comment Share on other sites More sharing options...
BackinBlack Posted April 19, 2021 Share Posted April 19, 2021 1 hour ago, Brian Lambert said: Just a thought, is there a capacitor (condenser) across the points? they can fail shorted when hot. I agree. I don't like guessing without seeing/hearing the engine running, but that would be my prime suspect. The magneto points, coils and condenser all hidden from view are rarely checked. Quote Link to comment Share on other sites More sharing options...
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